diff --git a/crates/blockifier_reexecution/src/main.rs b/crates/blockifier_reexecution/src/main.rs
index 8efd169f74..b1a15bd6a8 100644
--- a/crates/blockifier_reexecution/src/main.rs
+++ b/crates/blockifier_reexecution/src/main.rs
@@ -4,13 +4,13 @@ use blockifier_reexecution::state_reader::test_state_reader::{
 };
 use blockifier_reexecution::state_reader::utils::{
     get_block_numbers_for_reexecution,
+    guess_chain_id_from_node_url,
     reexecute_and_verify_correctness,
     write_block_reexecution_data_to_file,
     JSON_RPC_VERSION,
 };
 use clap::{Args, Parser, Subcommand};
 use starknet_api::block::BlockNumber;
-use starknet_api::core::ChainId;
 use starknet_gateway::config::RpcStateReaderConfig;
 
 /// BlockifierReexecution CLI.
@@ -99,14 +99,14 @@ fn main() {
             println!("Running RPC test for block number {block_number} using node url {node_url}.",);
 
             let config = RpcStateReaderConfig {
-                url: node_url,
+                url: node_url.clone(),
                 json_rpc_version: JSON_RPC_VERSION.to_string(),
             };
 
             reexecute_and_verify_correctness(ConsecutiveTestStateReaders::new(
                 BlockNumber(block_number - 1),
                 Some(config),
-                ChainId::Mainnet,
+                guess_chain_id_from_node_url(node_url.as_str()).unwrap(),
                 false,
             ));
 
@@ -124,8 +124,8 @@ fn main() {
             write_block_reexecution_data_to_file(
                 BlockNumber(block_number),
                 &full_file_path,
-                node_url,
-                ChainId::Mainnet,
+                node_url.clone(),
+                guess_chain_id_from_node_url(node_url.as_str()).unwrap(),
             );
         }
 
@@ -149,7 +149,7 @@ fn main() {
                     block_number,
                     &full_file_path,
                     node_url.clone(),
-                    ChainId::Mainnet,
+                    guess_chain_id_from_node_url(node_url.as_str()).unwrap(),
                 );
             }
         }
diff --git a/crates/blockifier_reexecution/src/state_reader/errors.rs b/crates/blockifier_reexecution/src/state_reader/errors.rs
index e2d5a0c1dc..62068142c9 100644
--- a/crates/blockifier_reexecution/src/state_reader/errors.rs
+++ b/crates/blockifier_reexecution/src/state_reader/errors.rs
@@ -9,6 +9,8 @@ use thiserror::Error;
 #[derive(Debug, Error)]
 #[allow(clippy::enum_variant_names)]
 pub enum ReexecutionError {
+    #[error("Cannot discern chain ID from URL: {0}")]
+    AmbiguousChainIdFromUrl(String),
     #[error(transparent)]
     Rpc(#[from] RPCStateReaderError),
     #[error(transparent)]
diff --git a/crates/blockifier_reexecution/src/state_reader/rpc_https_test.rs b/crates/blockifier_reexecution/src/state_reader/rpc_https_test.rs
index f2a47f3496..6e27718af3 100644
--- a/crates/blockifier_reexecution/src/state_reader/rpc_https_test.rs
+++ b/crates/blockifier_reexecution/src/state_reader/rpc_https_test.rs
@@ -34,6 +34,7 @@ use super::utils::RPC_NODE_URL;
 use crate::state_reader::compile::legacy_to_contract_class_v0;
 use crate::state_reader::reexecution_state_reader::ReexecutionStateReader;
 use crate::state_reader::test_state_reader::{ConsecutiveTestStateReaders, TestStateReader};
+use crate::state_reader::utils::guess_chain_id_from_node_url;
 
 const EXAMPLE_INVOKE_TX_HASH: &str =
     "0xa7c7db686c7f756ceb7ca85a759caef879d425d156da83d6a836f86851983";
@@ -87,14 +88,24 @@ pub fn get_test_rpc_config() -> RpcStateReaderConfig {
 }
 
 #[fixture]
-pub fn test_state_reader() -> TestStateReader {
+pub fn test_url() -> String {
+    get_test_url()
+}
+
+#[fixture]
+pub fn test_chain_id(test_url: String) -> ChainId {
+    guess_chain_id_from_node_url(test_url.as_str()).unwrap()
+}
+
+#[fixture]
+pub fn test_state_reader(test_chain_id: ChainId) -> TestStateReader {
     TestStateReader {
         rpc_state_reader: RpcStateReader {
             config: get_test_rpc_config(),
             block_id: get_test_block_id(),
         },
         retry_config: RetryConfig::default(),
-        chain_id: ChainId::Mainnet,
+        chain_id: test_chain_id,
         contract_class_mapping_dumper: Arc::new(Mutex::new(None)),
     }
 }
@@ -112,8 +123,9 @@ pub fn last_constructed_block(test_block_number: BlockNumber) -> BlockNumber {
 #[fixture]
 pub fn test_state_readers_last_and_current_block(
     last_constructed_block: BlockNumber,
+    test_chain_id: ChainId,
 ) -> ConsecutiveTestStateReaders {
-    ConsecutiveTestStateReaders::new(last_constructed_block, None, ChainId::Mainnet, false)
+    ConsecutiveTestStateReaders::new(last_constructed_block, None, test_chain_id, false)
 }
 
 /// Test that the block info can be retrieved from the RPC server.
@@ -232,7 +244,7 @@ pub fn test_get_statediff_rpc(test_state_reader: TestStateReader) {
 }
 
 #[rstest]
-#[case(test_block_number(test_state_reader()).0)]
+#[case(test_block_number(test_state_reader(test_chain_id(test_url()))).0)]
 #[case(EXAMPLE_DECLARE_V1_BLOCK_NUMBER)]
 #[case(EXAMPLE_DECLARE_V2_BLOCK_NUMBER)]
 #[case(EXAMPLE_DECLARE_V3_BLOCK_NUMBER)]
diff --git a/crates/blockifier_reexecution/src/state_reader/utils.rs b/crates/blockifier_reexecution/src/state_reader/utils.rs
index 40c94eb945..a6e90d8b87 100644
--- a/crates/blockifier_reexecution/src/state_reader/utils.rs
+++ b/crates/blockifier_reexecution/src/state_reader/utils.rs
@@ -21,6 +21,7 @@ use crate::state_reader::test_state_reader::{
     ConsecutiveStateReaders,
     ConsecutiveTestStateReaders,
     OfflineConsecutiveStateReaders,
+    ReexecutionResult,
     SerializableDataPrevBlock,
     SerializableOfflineReexecutionData,
 };
@@ -28,6 +29,20 @@ use crate::state_reader::test_state_reader::{
 pub const RPC_NODE_URL: &str = "https://free-rpc.nethermind.io/mainnet-juno/";
 pub const JSON_RPC_VERSION: &str = "2.0";
 
+pub fn guess_chain_id_from_node_url(node_url: &str) -> ReexecutionResult<ChainId> {
+    match (
+        node_url.contains("mainnet"),
+        node_url.contains("sepolia"),
+        node_url.contains("integration"),
+    ) {
+        (true, false, false) => Ok(ChainId::Mainnet),
+        (false, true, false) => Ok(ChainId::Sepolia),
+        // Integration URLs may contain the word "sepolia".
+        (false, _, true) => Ok(ChainId::IntegrationSepolia),
+        _ => Err(ReexecutionError::AmbiguousChainIdFromUrl(node_url.to_string())),
+    }
+}
+
 /// Returns the fee token addresses of mainnet.
 pub fn get_fee_token_addresses(chain_id: &ChainId) -> FeeTokenAddresses {
     match chain_id {