diff --git a/Makefile b/Makefile
index 641cec4c3..6b3339083 100644
--- a/Makefile
+++ b/Makefile
@@ -12,10 +12,20 @@ build: ## Build the project.
 clean: ## Clean the project.
 	cargo clean
 
+## Run all tests.
 .PHONY: test
-test: test-unit ## Run all tests.
+test: test-unit test-spec-integrated test-spec-modular
 
 .PHONY: test-unit
 test-unit: ## Run unit tests.
 	cargo install cargo-nextest --locked
 	cargo nextest run $(UNIT_TEST_ARGS)
+
+.PHONY: test-spec-integrated
+test-spec-integrated: ## Run spec tests in integrated mode
+	test/spec-tests/local/run-spec-tests.sh
+
+.PHONY: test-spec-modular
+test-spec-modular: ## Run spec tests in modular mode
+	test/spec-tests/remote/run-spec-tests.sh
+	
diff --git a/bin/rundler/src/cli/builder.rs b/bin/rundler/src/cli/builder.rs
index de1971a04..f93a43f41 100644
--- a/bin/rundler/src/cli/builder.rs
+++ b/bin/rundler/src/cli/builder.rs
@@ -3,7 +3,9 @@ use std::{collections::HashMap, net::SocketAddr, time::Duration};
 use anyhow::Context;
 use clap::Args;
 use ethers::types::H256;
-use rundler_builder::{self, BuilderEvent, BuilderTask, BuilderTaskArgs, LocalBuilderBuilder};
+use rundler_builder::{
+    self, BuilderEvent, BuilderEventKind, BuilderTask, BuilderTaskArgs, LocalBuilderBuilder,
+};
 use rundler_pool::RemotePoolClient;
 use rundler_sim::{MempoolConfig, PriorityFeeMode};
 use rundler_task::{
@@ -133,7 +135,8 @@ pub struct BuilderArgs {
     )]
     replacement_fee_percent_increase: u64,
 
-    ///
+    /// Maximum number of fee increases to apply to a transaction before giving
+    /// up and dropping.
     #[arg(
         long = "builder.max_fee_increases",
         name = "builder.max_fee_increases",
@@ -142,6 +145,15 @@ pub struct BuilderArgs {
         default_value = "7"
     )]
     max_fee_increases: u64,
+
+    /// The index offset to apply to the builder index
+    #[arg(
+        long = "builder_index_offset",
+        name = "builder_index_offset",
+        env = "BUILDER_INDEX_OFFSET",
+        default_value = "0"
+    )]
+    pub builder_index_offset: u64,
 }
 
 impl BuilderArgs {
@@ -201,6 +213,8 @@ impl BuilderArgs {
             replacement_fee_percent_increase: self.replacement_fee_percent_increase,
             max_fee_increases: self.max_fee_increases,
             remote_address,
+            num_bundle_builders: common.num_builders,
+            bundle_builder_index_offset: self.builder_index_offset,
         })
     }
 }
@@ -260,11 +274,11 @@ pub async fn run(builder_args: BuilderCliArgs, common_args: CommonArgs) -> anyho
 }
 
 pub fn is_nonspammy_event(event: &WithEntryPoint<BuilderEvent>) -> bool {
-    if let BuilderEvent::FormedBundle {
+    if let BuilderEventKind::FormedBundle {
         tx_details,
         fee_increase_count,
         ..
-    } = &event.event
+    } = &event.event.kind
     {
         if tx_details.is_none() && *fee_increase_count == 0 {
             return false;
diff --git a/bin/rundler/src/cli/mod.rs b/bin/rundler/src/cli/mod.rs
index df24e8d67..64d227cc6 100644
--- a/bin/rundler/src/cli/mod.rs
+++ b/bin/rundler/src/cli/mod.rs
@@ -205,6 +205,14 @@ pub struct CommonArgs {
         env = "MEMPOOL_CONFIG_PATH"
     )]
     pub mempool_config_path: Option<String>,
+
+    #[arg(
+        long = "num_builders",
+        name = "num_builders",
+        env = "NUM_BUILDERS",
+        default_value = "1"
+    )]
+    pub num_builders: u64,
 }
 
 const SIMULATION_GAS_OVERHEAD: u64 = 100_000;
diff --git a/bin/rundler/src/cli/pool.rs b/bin/rundler/src/cli/pool.rs
index b9db9efd6..7d51b0067 100644
--- a/bin/rundler/src/cli/pool.rs
+++ b/bin/rundler/src/cli/pool.rs
@@ -124,6 +124,8 @@ impl PoolArgs {
                 Ok(PoolConfig {
                     entry_point,
                     chain_id: common.chain_id,
+                    // Currently use the same shard count as the number of builders
+                    num_shards: common.num_builders,
                     max_userops_per_sender: self.max_userops_per_sender,
                     min_replacement_fee_increase_percentage: self
                         .min_replacement_fee_increase_percentage,
diff --git a/crates/builder/src/bundle_proposer.rs b/crates/builder/src/bundle_proposer.rs
index cbaf0db0e..fd5c60f72 100644
--- a/crates/builder/src/bundle_proposer.rs
+++ b/crates/builder/src/bundle_proposer.rs
@@ -73,6 +73,7 @@ where
     P: Provider,
     C: PoolServer,
 {
+    builder_index: u64,
     pool: C,
     simulator: S,
     entry_point: E,
@@ -109,7 +110,18 @@ where
         )?;
 
         // Limit the amount of gas in the bundle
-        let ops = self.limit_gas_in_bundle(ops);
+        tracing::debug!(
+            "Builder index: {}, starting bundle proposal with {} ops",
+            self.builder_index,
+            ops.len(),
+        );
+        let (ops, gas_limit) = self.limit_gas_in_bundle(ops);
+        tracing::debug!(
+            "Builder index: {}, bundle proposal after limit had {} ops and {:?} gas limit",
+            self.builder_index,
+            ops.len(),
+            gas_limit
+        );
 
         // Determine fees required for ops to be included in a bundle, and filter out ops that don't
         // meet the requirements. Simulate unfiltered ops.
@@ -122,16 +134,17 @@ where
                 {
                     true
                 } else {
-                    self.emit(BuilderEvent::SkippedOp {
-                        op_hash: self.op_hash(&op.uo),
-                        reason: SkipReason::InsufficientFees {
+                    self.emit(BuilderEvent::skipped_op(
+                        self.builder_index,
+                        self.op_hash(&op.uo),
+                        SkipReason::InsufficientFees {
                             required_fees: required_op_fees,
                             actual_fees: GasFees {
                                 max_fee_per_gas: op.uo.max_fee_per_gas,
                                 max_priority_fee_per_gas: op.uo.max_priority_fee_per_gas,
                             },
                         },
-                    });
+                    ));
                     false
                 }
             })
@@ -164,6 +177,12 @@ where
                 expected_storage.merge(&op.simulation.expected_storage)?;
             }
             if let Some(gas_estimate) = gas_estimate {
+                tracing::debug!(
+                    "Builder index: {}, bundle proposal succeeded with {} ops and {:?} gas limit",
+                    self.builder_index,
+                    context.iter_ops().count(),
+                    gas_estimate
+                );
                 return Ok(Bundle {
                     ops_per_aggregator: context.to_ops_per_aggregator(),
                     gas_estimate,
@@ -192,6 +211,7 @@ where
     C: PoolServer,
 {
     pub(crate) fn new(
+        builder_index: u64,
         pool: C,
         simulator: S,
         entry_point: E,
@@ -200,6 +220,7 @@ where
         event_sender: broadcast::Sender<WithEntryPoint<BuilderEvent>>,
     ) -> Self {
         Self {
+            builder_index,
             pool,
             simulator,
             entry_point,
@@ -250,10 +271,11 @@ where
             let simulation = match simulation {
                 Ok(simulation) => simulation,
                 Err(error) => {
-                    self.emit(BuilderEvent::RejectedOp {
-                        op_hash: self.op_hash(&op),
-                        reason: OpRejectionReason::FailedRevalidation { error },
-                    });
+                    self.emit(BuilderEvent::rejected_op(
+                        self.builder_index,
+                        self.op_hash(&op),
+                        OpRejectionReason::FailedRevalidation { error },
+                    ));
                     rejected_ops.push(op);
                     continue;
                 }
@@ -264,12 +286,13 @@ where
                 .valid_time_range
                 .contains(Timestamp::now(), TIME_RANGE_BUFFER)
             {
-                self.emit(BuilderEvent::SkippedOp {
-                    op_hash: self.op_hash(&op),
-                    reason: SkipReason::InvalidTimeRange {
+                self.emit(BuilderEvent::skipped_op(
+                    self.builder_index,
+                    self.op_hash(&op),
+                    SkipReason::InvalidTimeRange {
                         valid_range: simulation.valid_time_range,
                     },
-                });
+                ));
                 rejected_ops.push(op);
                 continue;
             }
@@ -282,10 +305,11 @@ where
                 // Exclude ops that access the sender of another op in the
                 // batch, but don't reject them (remove them from pool).
                 info!("Excluding op from {:?} because it accessed the address of another sender in the bundle.", op.sender);
-                self.emit(BuilderEvent::SkippedOp {
-                    op_hash: self.op_hash(&op),
-                    reason: SkipReason::AccessedOtherSender { other_sender },
-                });
+                self.emit(BuilderEvent::skipped_op(
+                    self.builder_index,
+                    self.op_hash(&op),
+                    SkipReason::AccessedOtherSender { other_sender },
+                ));
                 continue;
             }
             if let Some(paymaster) = op.paymaster() {
@@ -386,12 +410,13 @@ where
         match handle_ops_out {
             HandleOpsOut::Success => Ok(Some(gas)),
             HandleOpsOut::FailedOp(index, message) => {
-                self.emit(BuilderEvent::RejectedOp {
-                    op_hash: self.op_hash(context.get_op_at(index)?),
-                    reason: OpRejectionReason::FailedInBundle {
+                self.emit(BuilderEvent::rejected_op(
+                    self.builder_index,
+                    self.op_hash(context.get_op_at(index)?),
+                    OpRejectionReason::FailedInBundle {
                         message: Arc::new(message.clone()),
                     },
-                });
+                ));
                 self.process_failed_op(context, index, message).await?;
                 Ok(None)
             }
@@ -405,8 +430,17 @@ where
     }
 
     async fn get_ops_from_pool(&self) -> anyhow::Result<Vec<PoolOperation>> {
+        // Use builder's index as the shard index to ensure that two builders don't
+        // attempt to bundle the same operations.
+        //
+        // NOTE: this assumes that the pool server has as many shards as there
+        // are builders.
         self.pool
-            .get_ops(self.entry_point.address(), self.settings.max_bundle_size)
+            .get_ops(
+                self.entry_point.address(),
+                self.settings.max_bundle_size,
+                self.builder_index,
+            )
             .await
             .context("should get ops from pool")
     }
@@ -483,18 +517,26 @@ where
         Ok(())
     }
 
-    fn limit_gas_in_bundle(&self, ops: Vec<PoolOperation>) -> Vec<PoolOperation> {
+    fn limit_gas_in_bundle(&self, ops: Vec<PoolOperation>) -> (Vec<PoolOperation>, u64) {
         let mut gas_left = U256::from(self.settings.max_bundle_gas);
         let mut ops_in_bundle = Vec::new();
         for op in ops {
             let gas = gas::user_operation_execution_gas_limit(&op.uo, self.settings.chain_id);
             if gas_left < gas {
+                self.emit(BuilderEvent::skipped_op(
+                    self.builder_index,
+                    self.op_hash(&op.uo),
+                    SkipReason::GasLimit,
+                ));
                 continue;
             }
             gas_left -= gas;
             ops_in_bundle.push(op);
         }
-        ops_in_bundle
+        (
+            ops_in_bundle,
+            self.settings.max_bundle_gas - gas_left.as_u64(),
+        )
     }
 
     fn emit(&self, event: BuilderEvent) {
@@ -1191,7 +1233,7 @@ mod tests {
         let mut pool_client = MockPoolServer::new();
         pool_client
             .expect_get_ops()
-            .returning(move |_, _| Ok(ops.clone()));
+            .returning(move |_, _, _| Ok(ops.clone()));
 
         let simulations_by_op: HashMap<_, _> = mock_ops
             .into_iter()
@@ -1241,6 +1283,7 @@ mod tests {
             .returning(move |address, _| signatures_by_aggregator[&address]());
         let (event_sender, _) = broadcast::channel(16);
         let proposer = BundleProposerImpl::new(
+            0,
             pool_client,
             simulator,
             entry_point,
diff --git a/crates/builder/src/bundle_sender.rs b/crates/builder/src/bundle_sender.rs
index 5335de2ee..b803d0be0 100644
--- a/crates/builder/src/bundle_sender.rs
+++ b/crates/builder/src/bundle_sender.rs
@@ -14,7 +14,7 @@ use rundler_pool::PoolServer;
 use rundler_provider::EntryPoint;
 use rundler_sim::ExpectedStorage;
 use rundler_types::{Entity, GasFees, UserOperation};
-use rundler_utils::{emit::WithEntryPoint, math};
+use rundler_utils::emit::WithEntryPoint;
 use tokio::{
     join,
     sync::{broadcast, mpsc, oneshot},
@@ -28,9 +28,6 @@ use crate::{
     transaction_tracker::{SendResult, TrackerUpdate, TransactionTracker},
 };
 
-// Overhead on gas estimates to account for inaccuracies.
-const GAS_ESTIMATE_OVERHEAD_PERCENT: u64 = 10;
-
 #[async_trait]
 pub(crate) trait BundleSender: Send + Sync + 'static {
     async fn send_bundles_in_loop(&mut self);
@@ -50,6 +47,7 @@ where
     T: TransactionTracker,
     C: PoolServer,
 {
+    builder_index: u64,
     manual_bundling_mode: Arc<AtomicBool>,
     send_bundle_receiver: mpsc::Receiver<SendBundleRequest>,
     chain_id: u64,
@@ -188,7 +186,7 @@ where
                 } => info!("Bundle initially had {initial_op_count} operations, but after increasing gas fees {attempt_number} time(s) it was empty"),
                 SendBundleResult::StalledAtMaxFeeIncreases => warn!("Bundle failed to mine after {} fee increases", self.settings.max_fee_increases),
                 SendBundleResult::Error(error) => {
-                    BuilderMetrics::increment_bundle_txns_failed();
+                    BuilderMetrics::increment_bundle_txns_failed(self.builder_index);
                     error!("Failed to send bundle. Will retry next block: {error:#?}");
                 }
             }
@@ -211,6 +209,7 @@ where
 {
     #[allow(clippy::too_many_arguments)]
     pub(crate) fn new(
+        builder_index: u64,
         manual_bundling_mode: Arc<AtomicBool>,
         send_bundle_receiver: mpsc::Receiver<SendBundleRequest>,
         chain_id: u64,
@@ -224,6 +223,7 @@ where
         event_sender: broadcast::Sender<WithEntryPoint<BuilderEvent>>,
     ) -> Self {
         Self {
+            builder_index,
             manual_bundling_mode,
             send_bundle_receiver,
             chain_id,
@@ -257,7 +257,7 @@ where
                 attempt_number,
                 ..
             } => {
-                BuilderMetrics::increment_bundle_txns_success();
+                BuilderMetrics::increment_bundle_txns_success(self.builder_index);
                 if attempt_number == 0 {
                     info!("Bundle with hash {tx_hash:?} landed in block {block_number}");
                 } else {
@@ -266,17 +266,19 @@ where
             }
             TrackerUpdate::StillPendingAfterWait => (),
             TrackerUpdate::LatestTxDropped { nonce } => {
-                self.emit(BuilderEvent::LatestTransactionDropped {
-                    nonce: nonce.low_u64(),
-                });
-                BuilderMetrics::increment_bundle_txns_dropped();
+                self.emit(BuilderEvent::latest_transaction_dropped(
+                    self.builder_index,
+                    nonce.low_u64(),
+                ));
+                BuilderMetrics::increment_bundle_txns_dropped(self.builder_index);
                 info!("Previous transaction dropped by sender");
             }
             TrackerUpdate::NonceUsedForOtherTx { nonce } => {
-                self.emit(BuilderEvent::NonceUsedForOtherTransaction {
-                    nonce: nonce.low_u64(),
-                });
-                BuilderMetrics::increment_bundle_txns_nonce_used();
+                self.emit(BuilderEvent::nonce_used_for_other_transaction(
+                    self.builder_index,
+                    nonce.low_u64(),
+                ));
+                BuilderMetrics::increment_bundle_txns_nonce_used(self.builder_index);
                 info!("Nonce used by external transaction")
             }
         };
@@ -308,15 +310,16 @@ where
         let mut initial_op_count: Option<usize> = None;
         for fee_increase_count in 0..=self.settings.max_fee_increases {
             let Some(bundle_tx) = self.get_bundle_tx(nonce, required_fees).await? else {
-                self.emit(BuilderEvent::FormedBundle {
-                    tx_details: None,
-                    nonce: nonce.low_u64(),
+                self.emit(BuilderEvent::formed_bundle(
+                    self.builder_index,
+                    None,
+                    nonce.low_u64(),
                     fee_increase_count,
                     required_fees,
-                });
+                ));
                 return Ok(match initial_op_count {
                     Some(initial_op_count) => {
-                        BuilderMetrics::increment_bundle_txns_abandoned();
+                        BuilderMetrics::increment_bundle_txns_abandoned(self.builder_index);
                         SendBundleResult::NoOperationsAfterFeeIncreases {
                             initial_op_count,
                             attempt_number: fee_increase_count,
@@ -335,7 +338,7 @@ where
             }
             let current_fees = GasFees::from(&tx);
 
-            BuilderMetrics::increment_bundle_txns_sent();
+            BuilderMetrics::increment_bundle_txns_sent(self.builder_index);
             BuilderMetrics::set_current_fees(&current_fees);
 
             let send_result = self
@@ -345,16 +348,17 @@ where
             let update = match send_result {
                 SendResult::TrackerUpdate(update) => update,
                 SendResult::TxHash(tx_hash) => {
-                    self.emit(BuilderEvent::FormedBundle {
-                        tx_details: Some(BundleTxDetails {
+                    self.emit(BuilderEvent::formed_bundle(
+                        self.builder_index,
+                        Some(BundleTxDetails {
                             tx_hash,
                             tx,
                             op_hashes: Arc::new(op_hashes),
                         }),
-                        nonce: nonce.low_u64(),
+                        nonce.low_u64(),
                         fee_increase_count,
                         required_fees,
-                    });
+                    ));
                     self.transaction_tracker.wait_for_update().await?
                 }
             };
@@ -365,12 +369,13 @@ where
                     block_number,
                     attempt_number,
                 } => {
-                    self.emit(BuilderEvent::TransactionMined {
+                    self.emit(BuilderEvent::transaction_mined(
+                        self.builder_index,
                         tx_hash,
-                        nonce: nonce.low_u64(),
+                        nonce.low_u64(),
                         block_number,
-                    });
-                    BuilderMetrics::increment_bundle_txns_success();
+                    ));
+                    BuilderMetrics::increment_bundle_txns_success(self.builder_index);
                     return Ok(SendBundleResult::Success {
                         block_number,
                         attempt_number,
@@ -381,17 +386,19 @@ where
                     info!("Transaction not mined for several blocks")
                 }
                 TrackerUpdate::LatestTxDropped { nonce } => {
-                    self.emit(BuilderEvent::LatestTransactionDropped {
-                        nonce: nonce.low_u64(),
-                    });
-                    BuilderMetrics::increment_bundle_txns_dropped();
+                    self.emit(BuilderEvent::latest_transaction_dropped(
+                        self.builder_index,
+                        nonce.low_u64(),
+                    ));
+                    BuilderMetrics::increment_bundle_txns_dropped(self.builder_index);
                     info!("Previous transaction dropped by sender");
                 }
                 TrackerUpdate::NonceUsedForOtherTx { nonce } => {
-                    self.emit(BuilderEvent::NonceUsedForOtherTransaction {
-                        nonce: nonce.low_u64(),
-                    });
-                    BuilderMetrics::increment_bundle_txns_nonce_used();
+                    self.emit(BuilderEvent::nonce_used_for_other_transaction(
+                        self.builder_index,
+                        nonce.low_u64(),
+                    ));
+                    BuilderMetrics::increment_bundle_txns_nonce_used(self.builder_index);
                     bail!("nonce used by external transaction")
                 }
             };
@@ -400,12 +407,12 @@ where
                 current_fees.max_fee_per_gas,
                 current_fees.max_priority_fee_per_gas,
             );
-            BuilderMetrics::increment_bundle_txn_fee_increases();
+            BuilderMetrics::increment_bundle_txn_fee_increases(self.builder_index);
             required_fees = Some(
                 current_fees.increase_by_percent(self.settings.replacement_fee_percent_increase),
             );
         }
-        BuilderMetrics::increment_bundle_txns_abandoned();
+        BuilderMetrics::increment_bundle_txns_abandoned(self.builder_index);
         Ok(SendBundleResult::StalledAtMaxFeeIncreases)
     }
 
@@ -452,12 +459,11 @@ where
             bundle.rejected_ops.len(),
             bundle.rejected_entities.len()
         );
-        let gas = math::increase_by_percent(bundle.gas_estimate, GAS_ESTIMATE_OVERHEAD_PERCENT);
         let op_hashes: Vec<_> = bundle.iter_ops().map(|op| self.op_hash(op)).collect();
         let mut tx = self.entry_point.get_send_bundle_transaction(
             bundle.ops_per_aggregator,
             self.beneficiary,
-            gas,
+            bundle.gas_estimate,
             bundle.gas_fees,
         );
         tx.set_nonce(nonce);
@@ -502,34 +508,34 @@ where
 struct BuilderMetrics {}
 
 impl BuilderMetrics {
-    fn increment_bundle_txns_sent() {
-        metrics::increment_counter!("builder_bundle_txns_sent");
+    fn increment_bundle_txns_sent(builder_index: u64) {
+        metrics::increment_counter!("builder_bundle_txns_sent", "builder_index" => builder_index.to_string());
     }
 
-    fn increment_bundle_txns_success() {
-        metrics::increment_counter!("builder_bundle_txns_success");
+    fn increment_bundle_txns_success(builder_index: u64) {
+        metrics::increment_counter!("builder_bundle_txns_success", "builder_index" => builder_index.to_string());
     }
 
-    fn increment_bundle_txns_dropped() {
-        metrics::increment_counter!("builder_bundle_txns_dropped");
+    fn increment_bundle_txns_dropped(builder_index: u64) {
+        metrics::increment_counter!("builder_bundle_txns_dropped", "builder_index" => builder_index.to_string());
     }
 
     // used when we decide to stop trying a transaction
-    fn increment_bundle_txns_abandoned() {
-        metrics::increment_counter!("builder_bundle_txns_abandoned");
+    fn increment_bundle_txns_abandoned(builder_index: u64) {
+        metrics::increment_counter!("builder_bundle_txns_abandoned", "builder_index" => builder_index.to_string());
     }
 
     // used when sending a transaction fails
-    fn increment_bundle_txns_failed() {
-        metrics::increment_counter!("builder_bundle_txns_failed");
+    fn increment_bundle_txns_failed(builder_index: u64) {
+        metrics::increment_counter!("builder_bundle_txns_failed", "builder_index" => builder_index.to_string());
     }
 
-    fn increment_bundle_txns_nonce_used() {
-        metrics::increment_counter!("builder_bundle_txns_nonce_used");
+    fn increment_bundle_txns_nonce_used(builder_index: u64) {
+        metrics::increment_counter!("builder_bundle_txns_nonce_used", "builder_index" => builder_index.to_string());
     }
 
-    fn increment_bundle_txn_fee_increases() {
-        metrics::increment_counter!("builder_bundle_fee_increases");
+    fn increment_bundle_txn_fee_increases(builder_index: u64) {
+        metrics::increment_counter!("builder_bundle_fee_increases", "builder_index" => builder_index.to_string());
     }
 
     fn set_current_fees(fees: &GasFees) {
diff --git a/crates/builder/src/emit.rs b/crates/builder/src/emit.rs
index 85ee41fd6..6d416f980 100644
--- a/crates/builder/src/emit.rs
+++ b/crates/builder/src/emit.rs
@@ -7,7 +7,91 @@ use rundler_utils::strs;
 
 /// Builder event
 #[derive(Clone, Debug)]
-pub enum BuilderEvent {
+pub struct BuilderEvent {
+    /// Builder index that emitted the event
+    pub builder_index: u64,
+    /// Event kind
+    pub kind: BuilderEventKind,
+}
+
+impl BuilderEvent {
+    pub(crate) fn new(builder_index: u64, kind: BuilderEventKind) -> Self {
+        Self {
+            builder_index,
+            kind,
+        }
+    }
+
+    pub(crate) fn formed_bundle(
+        builder_index: u64,
+        tx_details: Option<BundleTxDetails>,
+        nonce: u64,
+        fee_increase_count: u64,
+        required_fees: Option<GasFees>,
+    ) -> Self {
+        Self::new(
+            builder_index,
+            BuilderEventKind::FormedBundle {
+                tx_details,
+                nonce,
+                fee_increase_count,
+                required_fees,
+            },
+        )
+    }
+
+    pub(crate) fn transaction_mined(
+        builder_index: u64,
+        tx_hash: H256,
+        nonce: u64,
+        block_number: u64,
+    ) -> Self {
+        Self::new(
+            builder_index,
+            BuilderEventKind::TransactionMined {
+                tx_hash,
+                nonce,
+                block_number,
+            },
+        )
+    }
+
+    pub(crate) fn latest_transaction_dropped(builder_index: u64, nonce: u64) -> Self {
+        Self::new(
+            builder_index,
+            BuilderEventKind::LatestTransactionDropped { nonce },
+        )
+    }
+
+    pub(crate) fn nonce_used_for_other_transaction(builder_index: u64, nonce: u64) -> Self {
+        Self::new(
+            builder_index,
+            BuilderEventKind::NonceUsedForOtherTransaction { nonce },
+        )
+    }
+
+    pub(crate) fn skipped_op(builder_index: u64, op_hash: H256, reason: SkipReason) -> Self {
+        Self::new(
+            builder_index,
+            BuilderEventKind::SkippedOp { op_hash, reason },
+        )
+    }
+
+    pub(crate) fn rejected_op(
+        builder_index: u64,
+        op_hash: H256,
+        reason: OpRejectionReason,
+    ) -> Self {
+        Self::new(
+            builder_index,
+            BuilderEventKind::RejectedOp { op_hash, reason },
+        )
+    }
+}
+
+/// BuilderEventKind
+#[derive(Clone, Debug)]
+pub enum BuilderEventKind {
     /// A bundle was formed
     FormedBundle {
         /// Details of the transaction that was sent
@@ -79,6 +163,8 @@ pub enum SkipReason {
         required_fees: GasFees,
         actual_fees: GasFees,
     },
+    /// Bundle ran out of space by gas limit to include the operation
+    GasLimit,
 }
 
 /// Reason for rejecting an operation from a bundle
@@ -92,8 +178,8 @@ pub enum OpRejectionReason {
 
 impl Display for BuilderEvent {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        match self {
-            BuilderEvent::FormedBundle {
+        match &self.kind {
+            BuilderEventKind::FormedBundle {
                 tx_details,
                 nonce,
                 fee_increase_count,
@@ -117,6 +203,7 @@ impl Display for BuilderEvent {
                             f,
                             concat!(
                                 "Bundle transaction sent!",
+                                "    Builder index: {:?}",
                                 "    Transaction hash: {:?}",
                                 "    Nonce: {}",
                                 "    Fee increases: {}",
@@ -124,6 +211,7 @@ impl Display for BuilderEvent {
                                 "    Required maxPriorityFeePerGas: {}",
                                 "    Op hashes: {}",
                             ),
+                            self.builder_index,
                             tx_details.tx_hash,
                             nonce,
                             fee_increase_count,
@@ -136,11 +224,13 @@ impl Display for BuilderEvent {
                         f,
                         concat!(
                             "Bundle was empty.",
+                            "    Builder index: {:?}",
                             "    Nonce: {}",
                             "    Fee increases: {}",
                             "    Required maxFeePerGas: {}",
                             "    Required maxPriorityFeePerGas: {}",
                         ),
+                        self.builder_index,
                         nonce,
                         fee_increase_count,
                         required_max_fee_per_gas,
@@ -148,7 +238,7 @@ impl Display for BuilderEvent {
                     ),
                 }
             }
-            BuilderEvent::TransactionMined {
+            BuilderEventKind::TransactionMined {
                 tx_hash,
                 nonce,
                 block_number,
@@ -156,26 +246,28 @@ impl Display for BuilderEvent {
                 f,
                 concat!(
                     "Transaction mined!",
+                    "    Builder index: {:?}",
                     "    Transaction hash: {:?}",
                     "    Nonce: {}",
                     "    Block number: {}",
                 ),
-                tx_hash, nonce, block_number,
+                self.builder_index, tx_hash, nonce, block_number,
             ),
-            BuilderEvent::LatestTransactionDropped { nonce } => {
+            BuilderEventKind::LatestTransactionDropped { nonce } => {
                 write!(
                     f,
-                    "Latest transaction dropped. Higher fees are needed.    Nonce: {nonce}"
+                    "Latest transaction dropped. Higher fees are needed.   Builder index: {:?}    Nonce: {nonce}",
+                    self.builder_index
                 )
             }
-            BuilderEvent::NonceUsedForOtherTransaction { nonce } => {
-                write!(f, "Transaction failed because nonce was used by another transaction outside of this Rundler.    Nonce: {nonce}")
+            BuilderEventKind::NonceUsedForOtherTransaction { nonce } => {
+                write!(f, "Transaction failed because nonce was used by another transaction outside of this Rundler.   Builder index: {:?}    Nonce: {nonce}", self.builder_index)
             }
-            BuilderEvent::SkippedOp { op_hash, reason } => {
-                write!(f, "Op skipped in bundle (but remains in pool).    Op hash: {op_hash:?}    Reason: {reason:?}")
+            BuilderEventKind::SkippedOp { op_hash, reason } => {
+                write!(f, "Op skipped in bundle (but remains in pool).   Builder index: {:?}    Op hash: {op_hash:?}    Reason: {reason:?}", self.builder_index)
             }
-            BuilderEvent::RejectedOp { op_hash, reason } => {
-                write!(f, "Op rejected from bundle and removed from pool.    Op hash: {op_hash:?}    Reason: {reason:?}")
+            BuilderEventKind::RejectedOp { op_hash, reason } => {
+                write!(f, "Op rejected from bundle and removed from pool.   Builder index: {:?}    Op hash: {op_hash:?}    Reason: {reason:?}", self.builder_index)
             }
         }
     }
diff --git a/crates/builder/src/lib.rs b/crates/builder/src/lib.rs
index 9bbc22467..9bb110bf0 100644
--- a/crates/builder/src/lib.rs
+++ b/crates/builder/src/lib.rs
@@ -10,7 +10,7 @@ mod bundle_proposer;
 mod bundle_sender;
 
 mod emit;
-pub use emit::BuilderEvent;
+pub use emit::{BuilderEvent, BuilderEventKind};
 
 mod sender;
 
diff --git a/crates/builder/src/server/local.rs b/crates/builder/src/server/local.rs
index 792134f47..a75ab92bd 100644
--- a/crates/builder/src/server/local.rs
+++ b/crates/builder/src/server/local.rs
@@ -45,14 +45,14 @@ impl LocalBuilderBuilder {
     pub fn run(
         self,
         manual_bundling_mode: Arc<AtomicBool>,
-        send_bundle_requester: mpsc::Sender<SendBundleRequest>,
+        send_bundle_requesters: Vec<mpsc::Sender<SendBundleRequest>>,
         entry_points: Vec<Address>,
         shutdown_token: CancellationToken,
     ) -> JoinHandle<anyhow::Result<()>> {
         let mut runner = LocalBuilderServerRunner::new(
             self.req_receiver,
             manual_bundling_mode,
-            send_bundle_requester,
+            send_bundle_requesters,
             entry_points,
         );
         tokio::spawn(async move { runner.run(shutdown_token).await })
@@ -67,7 +67,7 @@ pub struct LocalBuilderHandle {
 
 struct LocalBuilderServerRunner {
     req_receiver: mpsc::Receiver<ServerRequest>,
-    send_bundle_requester: mpsc::Sender<SendBundleRequest>,
+    send_bundle_requesters: Vec<mpsc::Sender<SendBundleRequest>>,
     manual_bundling_mode: Arc<AtomicBool>,
     entry_points: Vec<Address>,
 }
@@ -138,13 +138,13 @@ impl LocalBuilderServerRunner {
     fn new(
         req_receiver: mpsc::Receiver<ServerRequest>,
         manual_bundling_mode: Arc<AtomicBool>,
-        send_bundle_requester: mpsc::Sender<SendBundleRequest>,
+        send_bundle_requesters: Vec<mpsc::Sender<SendBundleRequest>>,
         entry_points: Vec<Address>,
     ) -> Self {
         Self {
             req_receiver,
             manual_bundling_mode,
-            send_bundle_requester,
+            send_bundle_requesters,
             entry_points,
         }
     }
@@ -166,10 +166,12 @@ impl LocalBuilderServerRunner {
                             ServerRequestKind::DebugSendBundleNow => {
                                 if !self.manual_bundling_mode.load(Ordering::Relaxed) {
                                     break 'a Err(anyhow::anyhow!("bundling mode is not manual").into())
+                                } else if self.send_bundle_requesters.len() != 1 {
+                                    break 'a Err(anyhow::anyhow!("more than 1 bundle builder not supported in debug mode").into())
                                 }
 
                                 let (tx, rx) = oneshot::channel();
-                                match self.send_bundle_requester.send(SendBundleRequest{
+                                match self.send_bundle_requesters[0].send(SendBundleRequest{
                                     responder: tx
                                 }).await {
                                     Ok(()) => {},
diff --git a/crates/builder/src/task.rs b/crates/builder/src/task.rs
index 55567529d..293e32827 100644
--- a/crates/builder/src/task.rs
+++ b/crates/builder/src/task.rs
@@ -7,7 +7,10 @@ use std::{
 
 use anyhow::{bail, Context};
 use async_trait::async_trait;
-use ethers::types::{Address, H256};
+use ethers::{
+    providers::{JsonRpcClient, Provider},
+    types::{Address, H256},
+};
 use ethers_signers::Signer;
 use rundler_pool::PoolServer;
 use rundler_sim::{
@@ -30,7 +33,7 @@ use tracing::info;
 
 use crate::{
     bundle_proposer::{self, BundleProposerImpl},
-    bundle_sender::{self, BundleSender, BundleSenderImpl},
+    bundle_sender::{self, BundleSender, BundleSenderImpl, SendBundleRequest},
     emit::BuilderEvent,
     sender::get_sender,
     server::{spawn_remote_builder_server, LocalBuilderBuilder},
@@ -88,6 +91,10 @@ pub struct Args {
     pub max_fee_increases: u64,
     /// Address to bind the remote builder server to, if any. If none, no server is starter.
     pub remote_address: Option<SocketAddr>,
+    /// Number of bundle builders to start
+    pub num_bundle_builders: u64,
+    /// Index offset for bundle builders
+    pub bundle_builder_index_offset: u64,
 }
 
 /// Builder task
@@ -108,6 +115,93 @@ where
         tracing::info!("Mempool config: {:?}", self.args.mempool_configs);
 
         let provider = eth::new_provider(&self.args.rpc_url, self.args.eth_poll_interval)?;
+        let manual_bundling_mode = Arc::new(AtomicBool::new(false));
+
+        let mut spawn_guards = vec![];
+        let mut send_bundle_txs = vec![];
+        for i in 0..self.args.num_bundle_builders {
+            let (spawn_guard, send_bundle_tx) = self
+                .create_bundle_builder(
+                    i + self.args.bundle_builder_index_offset,
+                    Arc::clone(&manual_bundling_mode),
+                    Arc::clone(&provider),
+                )
+                .await?;
+            spawn_guards.push(spawn_guard);
+            send_bundle_txs.push(send_bundle_tx);
+        }
+
+        let builder_handle = self.builder_builder.get_handle();
+        let builder_runnder_handle = self.builder_builder.run(
+            manual_bundling_mode,
+            send_bundle_txs,
+            vec![self.args.entry_point_address],
+            shutdown_token.clone(),
+        );
+
+        let remote_handle = match self.args.remote_address {
+            Some(addr) => {
+                spawn_remote_builder_server(
+                    addr,
+                    self.args.chain_id,
+                    builder_handle,
+                    shutdown_token,
+                )
+                .await?
+            }
+            None => tokio::spawn(async { Ok(()) }),
+        };
+
+        info!("Started bundle builder");
+
+        match try_join!(
+            handle::flatten_handle(builder_runnder_handle),
+            handle::flatten_handle(remote_handle),
+        ) {
+            Ok(_) => {
+                tracing::info!("Builder server shutdown");
+                Ok(())
+            }
+            Err(e) => {
+                tracing::error!("Builder server error: {e:?}");
+                bail!("Builder server error: {e:?}")
+            }
+        }
+    }
+}
+
+impl<P> BuilderTask<P>
+where
+    P: PoolServer + Clone,
+{
+    /// Create a new builder task
+    pub fn new(
+        args: Args,
+        event_sender: broadcast::Sender<WithEntryPoint<BuilderEvent>>,
+        builder_builder: LocalBuilderBuilder,
+        pool: P,
+    ) -> Self {
+        Self {
+            args,
+            event_sender,
+            builder_builder,
+            pool,
+        }
+    }
+
+    /// Convert this task into a boxed task
+    pub fn boxed(self) -> Box<dyn Task> {
+        Box::new(self)
+    }
+
+    async fn create_bundle_builder<C: JsonRpcClient + 'static>(
+        &self,
+        index: u64,
+        manual_bundling_mode: Arc<AtomicBool>,
+        provider: Arc<Provider<C>>,
+    ) -> anyhow::Result<(SpawnGuard, mpsc::Sender<SendBundleRequest>)> {
+        let (send_bundle_tx, send_bundle_rx) = mpsc::channel(1);
+
         let signer = if let Some(pk) = &self.args.private_key {
             info!("Using local signer");
             BundlerSigner::Local(
@@ -184,10 +278,9 @@ where
             replacement_fee_percent_increase: self.args.replacement_fee_percent_increase,
             max_fee_increases: self.args.max_fee_increases,
         };
-        let manual_bundling_mode = Arc::new(AtomicBool::new(false));
-        let (send_bundle_tx, send_bundle_rx) = mpsc::channel(1);
 
         let proposer = BundleProposerImpl::new(
+            index,
             self.pool.clone(),
             simulator,
             entry_point.clone(),
@@ -196,6 +289,7 @@ where
             self.event_sender.clone(),
         );
         let mut builder = BundleSenderImpl::new(
+            index,
             manual_bundling_mode.clone(),
             send_bundle_rx,
             self.args.chain_id,
@@ -204,74 +298,14 @@ where
             proposer,
             entry_point,
             transaction_tracker,
-            self.pool,
+            self.pool.clone(),
             builder_settings,
             self.event_sender.clone(),
         );
 
-        let _builder_loop_guard =
-            { SpawnGuard::spawn_with_guard(async move { builder.send_bundles_in_loop().await }) };
-
-        let builder_handle = self.builder_builder.get_handle();
-        let builder_runnder_handle = self.builder_builder.run(
-            manual_bundling_mode,
+        Ok((
+            SpawnGuard::spawn_with_guard(async move { builder.send_bundles_in_loop().await }),
             send_bundle_tx,
-            vec![self.args.entry_point_address],
-            shutdown_token.clone(),
-        );
-
-        let remote_handle = match self.args.remote_address {
-            Some(addr) => {
-                spawn_remote_builder_server(
-                    addr,
-                    self.args.chain_id,
-                    builder_handle,
-                    shutdown_token,
-                )
-                .await?
-            }
-            None => tokio::spawn(async { Ok(()) }),
-        };
-
-        info!("Started bundle builder");
-
-        match try_join!(
-            handle::flatten_handle(builder_runnder_handle),
-            handle::flatten_handle(remote_handle),
-        ) {
-            Ok(_) => {
-                tracing::info!("Builder server shutdown");
-                Ok(())
-            }
-            Err(e) => {
-                tracing::error!("Builder server error: {e:?}");
-                bail!("Builder server error: {e:?}")
-            }
-        }
-    }
-}
-
-impl<P> BuilderTask<P>
-where
-    P: PoolServer + Clone,
-{
-    /// Create a new builder task
-    pub fn new(
-        args: Args,
-        event_sender: broadcast::Sender<WithEntryPoint<BuilderEvent>>,
-        builder_builder: LocalBuilderBuilder,
-        pool: P,
-    ) -> Self {
-        Self {
-            args,
-            event_sender,
-            builder_builder,
-            pool,
-        }
-    }
-
-    /// Convert this task into a boxed task
-    pub fn boxed(self) -> Box<dyn Task> {
-        Box::new(self)
+        ))
     }
 }
diff --git a/crates/pool/proto/op_pool/op_pool.proto b/crates/pool/proto/op_pool/op_pool.proto
index 1e29ea935..3ec7d2ed8 100644
--- a/crates/pool/proto/op_pool/op_pool.proto
+++ b/crates/pool/proto/op_pool/op_pool.proto
@@ -153,6 +153,8 @@ message GetOpsRequest {
   bytes entry_point = 1;
   // The maximum number of UserOperations to return
   uint64 max_ops = 2;
+  // The mempool shard num retrieve UserOperations from
+  uint64 shard_index = 3; 
 }
 message GetOpsResponse {
   oneof result {
diff --git a/crates/pool/src/mempool/mod.rs b/crates/pool/src/mempool/mod.rs
index 0a66223db..259c62473 100644
--- a/crates/pool/src/mempool/mod.rs
+++ b/crates/pool/src/mempool/mod.rs
@@ -47,16 +47,22 @@ pub trait Mempool: Send + Sync + 'static {
     /// Removes a set of operations from the pool.
     fn remove_operations(&self, hashes: &[H256]);
 
-    /// Removes all operations assocaited with a given entity from the pool.
+    /// Removes all operations associated with a given entity from the pool.
     fn remove_entity(&self, entity: Entity);
 
     /// Returns the best operations from the pool.
     ///
     /// Returns the best operations from the pool based on their gas bids up to
-    /// the specified maximum number of operations.
+    /// the specified maximum number of operations, limiting to one per sender.
     ///
-    /// NOTE: Will only return one operation per sender.
-    fn best_operations(&self, max: usize) -> Vec<Arc<PoolOperation>>;
+    /// The `shard_index` is used to divide the mempool into disjoint shards to ensure
+    /// that two bundle builders don't attempt to but bundle the same operations. If
+    /// the supplied `shard_index` does not exist, the call will error.
+    fn best_operations(
+        &self,
+        max: usize,
+        shard_index: u64,
+    ) -> MempoolResult<Vec<Arc<PoolOperation>>>;
 
     /// Returns the all operations from the pool up to a max size
     fn all_operations(&self, max: usize) -> Vec<Arc<PoolOperation>>;
@@ -89,7 +95,7 @@ pub struct PoolConfig {
     pub max_size_of_pool_bytes: usize,
     /// Operations that are always banned from the mempool
     pub blocklist: Option<HashSet<Address>>,
-    /// Operations that are allways allowed in the mempool, regardless of reputation
+    /// Operations that are always allowed in the mempool, regardless of reputation
     pub allowlist: Option<HashSet<Address>>,
     /// Settings for precheck validation
     pub precheck_settings: PrecheckSettings,
@@ -97,6 +103,11 @@ pub struct PoolConfig {
     pub sim_settings: SimulationSettings,
     /// Configuration for the mempool channels, by channel ID
     pub mempool_channel_configs: HashMap<H256, MempoolConfig>,
+    /// Number of mempool shards to use. A mempool shard is a disjoint subset of the mempool
+    /// that is used to ensure that two bundle builders don't attempt to but bundle the same
+    /// operations. The mempool is divided into shards by taking the hash of the operation
+    /// and modding it by the number of shards.
+    pub num_shards: u64,
 }
 
 /// Origin of an operation.
@@ -156,7 +167,7 @@ impl PoolOperation {
         }
     }
 
-    /// Returns an iterator over all entities that are included in this opearation.
+    /// Returns an iterator over all entities that are included in this operation.
     pub fn entities(&'_ self) -> impl Iterator<Item = Entity> + '_ {
         EntityType::iter().filter_map(|entity| {
             self.entity_address(entity)
@@ -164,7 +175,7 @@ impl PoolOperation {
         })
     }
 
-    /// Returns an iterator over all staked entities that are included in this opearation.
+    /// Returns an iterator over all staked entities that are included in this operation.
     pub fn staked_entities(&'_ self) -> impl Iterator<Item = Entity> + '_ {
         EntityType::iter()
             .filter(|entity| self.is_staked(*entity))
diff --git a/crates/pool/src/mempool/uo_pool.rs b/crates/pool/src/mempool/uo_pool.rs
index a41a13168..d40637762 100644
--- a/crates/pool/src/mempool/uo_pool.rs
+++ b/crates/pool/src/mempool/uo_pool.rs
@@ -3,7 +3,7 @@ use std::{
     sync::Arc,
 };
 
-use ethers::types::{Address, H256};
+use ethers::types::{Address, H256, U256};
 use itertools::Itertools;
 use parking_lot::RwLock;
 use rundler_sim::{Prechecker, Simulator};
@@ -35,6 +35,7 @@ const THROTTLED_OPS_BLOCK_LIMIT: u64 = 10;
 pub(crate) struct UoPool<R: ReputationManager, P: Prechecker, S: Simulator> {
     entry_point: Address,
     chain_id: u64,
+    num_shards: u64,
     reputation: Arc<R>,
     state: RwLock<UoPoolState>,
     event_sender: broadcast::Sender<WithEntryPoint<OpPoolEvent>>,
@@ -64,6 +65,7 @@ where
         Self {
             entry_point: config.entry_point,
             chain_id: config.chain_id,
+            num_shards: config.num_shards,
             reputation,
             state: RwLock::new(UoPoolState {
                 pool: PoolInner::new(config.into()),
@@ -314,20 +316,34 @@ where
         UoPoolMetrics::increment_removed_entities(self.entry_point);
     }
 
-    fn best_operations(&self, max: usize) -> Vec<Arc<PoolOperation>> {
+    fn best_operations(
+        &self,
+        max: usize,
+        shard_index: u64,
+    ) -> MempoolResult<Vec<Arc<PoolOperation>>> {
+        if shard_index >= self.num_shards {
+            Err(anyhow::anyhow!("Invalid shard ID"))?;
+        }
+
         // get the best operations from the pool
         let ordered_ops = self.state.read().pool.best_operations();
         // keep track of senders to avoid sending multiple ops from the same sender
         let mut senders = HashSet::<Address>::new();
 
-        ordered_ops
+        Ok(ordered_ops
             .into_iter()
             .filter(|op| {
+                // short-circuit the mod if there is only 1 shard
+                ((self.num_shards == 1) ||
+                (U256::from_little_endian(op.uo.sender.as_bytes())
+                        .div_mod(self.num_shards.into())
+                        .1
+                        == shard_index.into())) &&
                 // filter out ops from senders we've already seen
                 senders.insert(op.uo.sender)
             })
             .take(max)
-            .collect()
+            .collect())
     }
 
     fn all_operations(&self, max: usize) -> Vec<Arc<PoolOperation>> {
@@ -393,9 +409,9 @@ mod tests {
             .add_operation(OperationOrigin::Local, op.op)
             .await
             .unwrap();
-        check_ops(pool.best_operations(1), uos);
+        check_ops(pool.best_operations(1, 0).unwrap(), uos);
         pool.remove_operations(&[hash]);
-        assert_eq!(pool.best_operations(1), vec![]);
+        assert_eq!(pool.best_operations(1, 0).unwrap(), vec![]);
     }
 
     #[tokio::test]
@@ -416,9 +432,9 @@ mod tests {
                 .unwrap();
             hashes.push(hash);
         }
-        check_ops(pool.best_operations(3), uos);
+        check_ops(pool.best_operations(3, 0).unwrap(), uos);
         pool.remove_operations(&hashes);
-        assert_eq!(pool.best_operations(3), vec![]);
+        assert_eq!(pool.best_operations(3, 0).unwrap(), vec![]);
     }
 
     #[tokio::test]
@@ -437,9 +453,9 @@ mod tests {
                 .await
                 .unwrap();
         }
-        check_ops(pool.best_operations(3), uos);
+        check_ops(pool.best_operations(3, 0).unwrap(), uos);
         pool.clear();
-        assert_eq!(pool.best_operations(3), vec![]);
+        assert_eq!(pool.best_operations(3, 0).unwrap(), vec![]);
     }
 
     #[tokio::test]
@@ -450,7 +466,7 @@ mod tests {
             create_op(Address::random(), 0, 1),
         ])
         .await;
-        check_ops(pool.best_operations(3), uos.clone());
+        check_ops(pool.best_operations(3, 0).unwrap(), uos.clone());
 
         pool.on_chain_update(&ChainUpdate {
             latest_block_number: 1,
@@ -466,7 +482,7 @@ mod tests {
             unmined_ops: vec![],
         });
 
-        check_ops(pool.best_operations(3), uos[1..].to_vec());
+        check_ops(pool.best_operations(3, 0).unwrap(), uos[1..].to_vec());
     }
 
     #[tokio::test]
@@ -477,7 +493,7 @@ mod tests {
             create_op(Address::random(), 0, 1),
         ])
         .await;
-        check_ops(pool.best_operations(3), uos.clone());
+        check_ops(pool.best_operations(3, 0).unwrap(), uos.clone());
 
         pool.on_chain_update(&ChainUpdate {
             latest_block_number: 1,
@@ -492,7 +508,10 @@ mod tests {
             }],
             unmined_ops: vec![],
         });
-        check_ops(pool.best_operations(3), uos.clone()[1..].to_vec());
+        check_ops(
+            pool.best_operations(3, 0).unwrap(),
+            uos.clone()[1..].to_vec(),
+        );
 
         pool.on_chain_update(&ChainUpdate {
             latest_block_number: 1,
@@ -507,7 +526,7 @@ mod tests {
                 nonce: uos[0].nonce,
             }],
         });
-        check_ops(pool.best_operations(3), uos);
+        check_ops(pool.best_operations(3, 0).unwrap(), uos);
     }
 
     #[tokio::test]
@@ -518,7 +537,7 @@ mod tests {
             create_op(Address::random(), 0, 1),
         ])
         .await;
-        check_ops(pool.best_operations(3), uos.clone());
+        check_ops(pool.best_operations(3, 0).unwrap(), uos.clone());
 
         pool.on_chain_update(&ChainUpdate {
             latest_block_number: 1,
@@ -534,7 +553,7 @@ mod tests {
             unmined_ops: vec![],
         });
 
-        check_ops(pool.best_operations(3), uos);
+        check_ops(pool.best_operations(3, 0).unwrap(), uos);
     }
 
     #[tokio::test]
@@ -547,7 +566,7 @@ mod tests {
         ])
         .await;
         // Only return 1 op per sender
-        check_ops(pool.best_operations(3), vec![uos[0].clone()]);
+        check_ops(pool.best_operations(3, 0).unwrap(), vec![uos[0].clone()]);
 
         let rep = pool.dump_reputation();
         assert_eq!(rep.len(), 1);
@@ -593,9 +612,9 @@ mod tests {
         pool.add_operation(OperationOrigin::Local, uos[0].clone())
             .await
             .unwrap();
-        check_ops(pool.best_operations(1), vec![uos[0].clone()]);
+        check_ops(pool.best_operations(1, 0).unwrap(), vec![uos[0].clone()]);
 
-        // Second op should be thorottled
+        // Second op should be throttled
         let ret = pool
             .add_operation(OperationOrigin::Local, uos[1].clone())
             .await;
@@ -627,7 +646,7 @@ mod tests {
         pool.add_operation(OperationOrigin::Local, uos[1].clone())
             .await
             .unwrap();
-        check_ops(pool.best_operations(1), vec![uos[1].clone()]);
+        check_ops(pool.best_operations(1, 0).unwrap(), vec![uos[1].clone()]);
     }
 
     #[tokio::test]
@@ -669,7 +688,7 @@ mod tests {
             Err(MempoolError::PrecheckViolation(PrecheckViolation::InitCodeTooShort(_))) => {}
             _ => panic!("Expected InitCodeTooShort error"),
         }
-        assert_eq!(pool.best_operations(1), vec![]);
+        assert_eq!(pool.best_operations(1, 0).unwrap(), vec![]);
     }
 
     #[tokio::test]
@@ -689,7 +708,7 @@ mod tests {
             Err(MempoolError::SimulationViolation(SimulationViolation::DidNotRevert)) => {}
             _ => panic!("Expected DidNotRevert error"),
         }
-        assert_eq!(pool.best_operations(1), vec![]);
+        assert_eq!(pool.best_operations(1, 0).unwrap(), vec![]);
     }
 
     #[derive(Clone, Debug)]
@@ -739,6 +758,7 @@ mod tests {
             precheck_settings: PrecheckSettings::default(),
             sim_settings: SimulationSettings::default(),
             mempool_channel_configs: HashMap::new(),
+            num_shards: 1,
         };
         let (event_sender, _) = broadcast::channel(4);
         UoPool::new(args, reputation, event_sender, prechecker, simulator)
diff --git a/crates/pool/src/server/local.rs b/crates/pool/src/server/local.rs
index ca6e38e8c..71d653e6a 100644
--- a/crates/pool/src/server/local.rs
+++ b/crates/pool/src/server/local.rs
@@ -118,10 +118,16 @@ impl PoolServer for LocalPoolHandle {
         }
     }
 
-    async fn get_ops(&self, entry_point: Address, max_ops: u64) -> PoolResult<Vec<PoolOperation>> {
+    async fn get_ops(
+        &self,
+        entry_point: Address,
+        max_ops: u64,
+        shard_index: u64,
+    ) -> PoolResult<Vec<PoolOperation>> {
         let req = ServerRequestKind::GetOps {
             entry_point,
             max_ops,
+            shard_index,
         };
         let resp = self.send(req).await?;
         match resp {
@@ -256,10 +262,15 @@ where
         })
     }
 
-    fn get_ops(&self, entry_point: Address, max_ops: u64) -> PoolResult<Vec<PoolOperation>> {
+    fn get_ops(
+        &self,
+        entry_point: Address,
+        max_ops: u64,
+        shard_index: u64,
+    ) -> PoolResult<Vec<PoolOperation>> {
         let mempool = self.get_pool(entry_point)?;
         Ok(mempool
-            .best_operations(max_ops as usize)
+            .best_operations(max_ops as usize, shard_index)?
             .iter()
             .map(|op| (**op).clone())
             .collect())
@@ -365,8 +376,8 @@ where
                                 Err(e) => Err(e),
                             }
                         },
-                        ServerRequestKind::GetOps { entry_point, max_ops } => {
-                            match self.get_ops(entry_point, max_ops) {
+                        ServerRequestKind::GetOps { entry_point, max_ops, shard_index } => {
+                            match self.get_ops(entry_point, max_ops, shard_index) {
                                 Ok(ops) => Ok(ServerResponse::GetOps { ops }),
                                 Err(e) => Err(e),
                             }
@@ -439,6 +450,7 @@ enum ServerRequestKind {
     GetOps {
         entry_point: Address,
         max_ops: u64,
+        shard_index: u64,
     },
     RemoveOps {
         entry_point: Address,
diff --git a/crates/pool/src/server/mod.rs b/crates/pool/src/server/mod.rs
index 8382edbea..003ccaf8b 100644
--- a/crates/pool/src/server/mod.rs
+++ b/crates/pool/src/server/mod.rs
@@ -37,7 +37,12 @@ pub trait PoolServer: Send + Sync + 'static {
     async fn add_op(&self, entry_point: Address, op: UserOperation) -> PoolResult<H256>;
 
     /// Get operations from the pool
-    async fn get_ops(&self, entry_point: Address, max_ops: u64) -> PoolResult<Vec<PoolOperation>>;
+    async fn get_ops(
+        &self,
+        entry_point: Address,
+        max_ops: u64,
+        shard_index: u64,
+    ) -> PoolResult<Vec<PoolOperation>>;
 
     /// Remove operations from the pool by hash
     async fn remove_ops(&self, entry_point: Address, ops: Vec<H256>) -> PoolResult<()>;
diff --git a/crates/pool/src/server/remote/client.rs b/crates/pool/src/server/remote/client.rs
index 33bda3e58..d3024abde 100644
--- a/crates/pool/src/server/remote/client.rs
+++ b/crates/pool/src/server/remote/client.rs
@@ -141,13 +141,19 @@ impl PoolServer for RemotePoolClient {
         }
     }
 
-    async fn get_ops(&self, entry_point: Address, max_ops: u64) -> PoolResult<Vec<PoolOperation>> {
+    async fn get_ops(
+        &self,
+        entry_point: Address,
+        max_ops: u64,
+        shard_index: u64,
+    ) -> PoolResult<Vec<PoolOperation>> {
         let res = self
             .op_pool_client
             .clone()
             .get_ops(GetOpsRequest {
                 entry_point: entry_point.as_bytes().to_vec(),
                 max_ops,
+                shard_index,
             })
             .await?
             .into_inner()
diff --git a/crates/pool/src/server/remote/server.rs b/crates/pool/src/server/remote/server.rs
index 4d1d3b228..524e994c6 100644
--- a/crates/pool/src/server/remote/server.rs
+++ b/crates/pool/src/server/remote/server.rs
@@ -143,7 +143,11 @@ impl OpPool for OpPoolImpl {
         let req = request.into_inner();
         let ep = self.get_entry_point(&req.entry_point)?;
 
-        let resp = match self.local_pool.get_ops(ep, req.max_ops).await {
+        let resp = match self
+            .local_pool
+            .get_ops(ep, req.max_ops, req.shard_index)
+            .await
+        {
             Ok(ops) => GetOpsResponse {
                 result: Some(get_ops_response::Result::Success(GetOpsSuccess {
                     ops: ops.iter().map(MempoolOp::from).collect(),