diff --git a/examples/ethereum/client/client.go b/examples/ethereum/client/client.go
index a17abca..39c8f84 100644
--- a/examples/ethereum/client/client.go
+++ b/examples/ethereum/client/client.go
@@ -46,10 +46,10 @@ func (c *EthereumClient) ParseOps(
 	var ops []*RosettaTypes.Operation
 
 	// Compute fee operations
-	feeOps := services.FeeOps(tx)
+	feeOps := services.FeeOps(tx, sdkTypes.Currency)
 	ops = append(ops, feeOps...)
 
-	traceOps := services.TraceOps(tx.Trace, len(ops))
+	traceOps := services.TraceOps(tx.Trace, len(ops), sdkTypes.Currency)
 	ops = append(ops, traceOps...)
 
 	return ops, nil
diff --git a/mocks/client/graph_ql.go b/mocks/client/graph_ql.go
index 40596db..897986a 100644
--- a/mocks/client/graph_ql.go
+++ b/mocks/client/graph_ql.go
@@ -1,4 +1,4 @@
-// Code generated by mockery v0.0.0-dev. DO NOT EDIT.
+// Code generated by mockery v2.33.3. DO NOT EDIT.
 
 package client
 
@@ -18,13 +18,16 @@ func (_m *GraphQL) Query(ctx context.Context, input string) (string, error) {
 	ret := _m.Called(ctx, input)
 
 	var r0 string
+	var r1 error
+	if rf, ok := ret.Get(0).(func(context.Context, string) (string, error)); ok {
+		return rf(ctx, input)
+	}
 	if rf, ok := ret.Get(0).(func(context.Context, string) string); ok {
 		r0 = rf(ctx, input)
 	} else {
 		r0 = ret.Get(0).(string)
 	}
 
-	var r1 error
 	if rf, ok := ret.Get(1).(func(context.Context, string) error); ok {
 		r1 = rf(ctx, input)
 	} else {
@@ -33,3 +36,17 @@ func (_m *GraphQL) Query(ctx context.Context, input string) (string, error) {
 
 	return r0, r1
 }
+
+// NewGraphQL creates a new instance of GraphQL. It also registers a testing interface on the mock and a cleanup function to assert the mocks expectations.
+// The first argument is typically a *testing.T value.
+func NewGraphQL(t interface {
+	mock.TestingT
+	Cleanup(func())
+}) *GraphQL {
+	mock := &GraphQL{}
+	mock.Mock.Test(t)
+
+	t.Cleanup(func() { mock.AssertExpectations(t) })
+
+	return mock
+}
diff --git a/mocks/client/jsonrpc.go b/mocks/client/jsonrpc.go
index dcb314b..9519783 100644
--- a/mocks/client/jsonrpc.go
+++ b/mocks/client/jsonrpc.go
@@ -1,4 +1,4 @@
-// Code generated by mockery v0.0.0-dev. DO NOT EDIT.
+// Code generated by mockery v2.33.3. DO NOT EDIT.
 
 package client
 
@@ -49,3 +49,17 @@ func (_m *JSONRPC) CallContext(ctx context.Context, result interface{}, method s
 func (_m *JSONRPC) Close() {
 	_m.Called()
 }
+
+// NewJSONRPC creates a new instance of JSONRPC. It also registers a testing interface on the mock and a cleanup function to assert the mocks expectations.
+// The first argument is typically a *testing.T value.
+func NewJSONRPC(t interface {
+	mock.TestingT
+	Cleanup(func())
+}) *JSONRPC {
+	mock := &JSONRPC{}
+	mock.Mock.Test(t)
+
+	t.Cleanup(func() { mock.AssertExpectations(t) })
+
+	return mock
+}
diff --git a/mocks/services/client.go b/mocks/services/client.go
index 0b9dd63..28c9a1d 100644
--- a/mocks/services/client.go
+++ b/mocks/services/client.go
@@ -1,4 +1,4 @@
-// Code generated by mockery v0.0.0-dev. DO NOT EDIT.
+// Code generated by mockery v2.33.3. DO NOT EDIT.
 
 package services
 
@@ -14,6 +14,8 @@ import (
 
 	coretypes "github.com/ethereum/go-ethereum/core/types"
 
+	ethereum "github.com/ethereum/go-ethereum"
+
 	json "encoding/json"
 
 	mock "github.com/stretchr/testify/mock"
@@ -33,6 +35,10 @@ func (_m *Client) Balance(_a0 context.Context, _a1 *types.AccountIdentifier, _a2
 	ret := _m.Called(_a0, _a1, _a2, _a3)
 
 	var r0 *types.AccountBalanceResponse
+	var r1 error
+	if rf, ok := ret.Get(0).(func(context.Context, *types.AccountIdentifier, *types.PartialBlockIdentifier, []*types.Currency) (*types.AccountBalanceResponse, error)); ok {
+		return rf(_a0, _a1, _a2, _a3)
+	}
 	if rf, ok := ret.Get(0).(func(context.Context, *types.AccountIdentifier, *types.PartialBlockIdentifier, []*types.Currency) *types.AccountBalanceResponse); ok {
 		r0 = rf(_a0, _a1, _a2, _a3)
 	} else {
@@ -41,7 +47,6 @@ func (_m *Client) Balance(_a0 context.Context, _a1 *types.AccountIdentifier, _a2
 		}
 	}
 
-	var r1 error
 	if rf, ok := ret.Get(1).(func(context.Context, *types.AccountIdentifier, *types.PartialBlockIdentifier, []*types.Currency) error); ok {
 		r1 = rf(_a0, _a1, _a2, _a3)
 	} else {
@@ -70,13 +75,16 @@ func (_m *Client) BlockAuthor(ctx context.Context, blockIndex int64) (string, er
 	ret := _m.Called(ctx, blockIndex)
 
 	var r0 string
+	var r1 error
+	if rf, ok := ret.Get(0).(func(context.Context, int64) (string, error)); ok {
+		return rf(ctx, blockIndex)
+	}
 	if rf, ok := ret.Get(0).(func(context.Context, int64) string); ok {
 		r0 = rf(ctx, blockIndex)
 	} else {
 		r0 = ret.Get(0).(string)
 	}
 
-	var r1 error
 	if rf, ok := ret.Get(1).(func(context.Context, int64) error); ok {
 		r1 = rf(ctx, blockIndex)
 	} else {
@@ -119,11 +127,39 @@ func (_m *Client) CallContext(ctx context.Context, result interface{}, method st
 	return r0
 }
 
+// EstimateGas provides a mock function with given fields: ctx, msg
+func (_m *Client) EstimateGas(ctx context.Context, msg ethereum.CallMsg) (uint64, error) {
+	ret := _m.Called(ctx, msg)
+
+	var r0 uint64
+	var r1 error
+	if rf, ok := ret.Get(0).(func(context.Context, ethereum.CallMsg) (uint64, error)); ok {
+		return rf(ctx, msg)
+	}
+	if rf, ok := ret.Get(0).(func(context.Context, ethereum.CallMsg) uint64); ok {
+		r0 = rf(ctx, msg)
+	} else {
+		r0 = ret.Get(0).(uint64)
+	}
+
+	if rf, ok := ret.Get(1).(func(context.Context, ethereum.CallMsg) error); ok {
+		r1 = rf(ctx, msg)
+	} else {
+		r1 = ret.Error(1)
+	}
+
+	return r0, r1
+}
+
 // GetBlockReceipts provides a mock function with given fields: ctx, blockHash, txs, baseFee
 func (_m *Client) GetBlockReceipts(ctx context.Context, blockHash common.Hash, txs []client.RPCTransaction, baseFee *big.Int) ([]*client.RosettaTxReceipt, error) {
 	ret := _m.Called(ctx, blockHash, txs, baseFee)
 
 	var r0 []*client.RosettaTxReceipt
+	var r1 error
+	if rf, ok := ret.Get(0).(func(context.Context, common.Hash, []client.RPCTransaction, *big.Int) ([]*client.RosettaTxReceipt, error)); ok {
+		return rf(ctx, blockHash, txs, baseFee)
+	}
 	if rf, ok := ret.Get(0).(func(context.Context, common.Hash, []client.RPCTransaction, *big.Int) []*client.RosettaTxReceipt); ok {
 		r0 = rf(ctx, blockHash, txs, baseFee)
 	} else {
@@ -132,7 +168,6 @@ func (_m *Client) GetBlockReceipts(ctx context.Context, blockHash common.Hash, t
 		}
 	}
 
-	var r1 error
 	if rf, ok := ret.Get(1).(func(context.Context, common.Hash, []client.RPCTransaction, *big.Int) error); ok {
 		r1 = rf(ctx, blockHash, txs, baseFee)
 	} else {
@@ -147,13 +182,16 @@ func (_m *Client) GetContractCallGasLimit(ctx context.Context, toAddress string,
 	ret := _m.Called(ctx, toAddress, fromAddress, data)
 
 	var r0 uint64
+	var r1 error
+	if rf, ok := ret.Get(0).(func(context.Context, string, string, []byte) (uint64, error)); ok {
+		return rf(ctx, toAddress, fromAddress, data)
+	}
 	if rf, ok := ret.Get(0).(func(context.Context, string, string, []byte) uint64); ok {
 		r0 = rf(ctx, toAddress, fromAddress, data)
 	} else {
 		r0 = ret.Get(0).(uint64)
 	}
 
-	var r1 error
 	if rf, ok := ret.Get(1).(func(context.Context, string, string, []byte) error); ok {
 		r1 = rf(ctx, toAddress, fromAddress, data)
 	} else {
@@ -168,6 +206,10 @@ func (_m *Client) GetContractCurrency(addr common.Address, erc20 bool) (*client.
 	ret := _m.Called(addr, erc20)
 
 	var r0 *client.ContractCurrency
+	var r1 error
+	if rf, ok := ret.Get(0).(func(common.Address, bool) (*client.ContractCurrency, error)); ok {
+		return rf(addr, erc20)
+	}
 	if rf, ok := ret.Get(0).(func(common.Address, bool) *client.ContractCurrency); ok {
 		r0 = rf(addr, erc20)
 	} else {
@@ -176,7 +218,6 @@ func (_m *Client) GetContractCurrency(addr common.Address, erc20 bool) (*client.
 		}
 	}
 
-	var r1 error
 	if rf, ok := ret.Get(1).(func(common.Address, bool) error); ok {
 		r1 = rf(addr, erc20)
 	} else {
@@ -191,13 +232,16 @@ func (_m *Client) GetErc20TransferGasLimit(ctx context.Context, toAddress string
 	ret := _m.Called(ctx, toAddress, fromAddress, value, currency)
 
 	var r0 uint64
+	var r1 error
+	if rf, ok := ret.Get(0).(func(context.Context, string, string, *big.Int, *types.Currency) (uint64, error)); ok {
+		return rf(ctx, toAddress, fromAddress, value, currency)
+	}
 	if rf, ok := ret.Get(0).(func(context.Context, string, string, *big.Int, *types.Currency) uint64); ok {
 		r0 = rf(ctx, toAddress, fromAddress, value, currency)
 	} else {
 		r0 = ret.Get(0).(uint64)
 	}
 
-	var r1 error
 	if rf, ok := ret.Get(1).(func(context.Context, string, string, *big.Int, *types.Currency) error); ok {
 		r1 = rf(ctx, toAddress, fromAddress, value, currency)
 	} else {
@@ -212,6 +256,10 @@ func (_m *Client) GetGasPrice(_a0 context.Context, _a1 client.Options) (*big.Int
 	ret := _m.Called(_a0, _a1)
 
 	var r0 *big.Int
+	var r1 error
+	if rf, ok := ret.Get(0).(func(context.Context, client.Options) (*big.Int, error)); ok {
+		return rf(_a0, _a1)
+	}
 	if rf, ok := ret.Get(0).(func(context.Context, client.Options) *big.Int); ok {
 		r0 = rf(_a0, _a1)
 	} else {
@@ -220,7 +268,6 @@ func (_m *Client) GetGasPrice(_a0 context.Context, _a1 client.Options) (*big.Int
 		}
 	}
 
-	var r1 error
 	if rf, ok := ret.Get(1).(func(context.Context, client.Options) error); ok {
 		r1 = rf(_a0, _a1)
 	} else {
@@ -235,6 +282,10 @@ func (_m *Client) GetLoadedTransaction(ctx context.Context, request *types.Block
 	ret := _m.Called(ctx, request)
 
 	var r0 *client.LoadedTransaction
+	var r1 error
+	if rf, ok := ret.Get(0).(func(context.Context, *types.BlockTransactionRequest) (*client.LoadedTransaction, error)); ok {
+		return rf(ctx, request)
+	}
 	if rf, ok := ret.Get(0).(func(context.Context, *types.BlockTransactionRequest) *client.LoadedTransaction); ok {
 		r0 = rf(ctx, request)
 	} else {
@@ -243,7 +294,6 @@ func (_m *Client) GetLoadedTransaction(ctx context.Context, request *types.Block
 		}
 	}
 
-	var r1 error
 	if rf, ok := ret.Get(1).(func(context.Context, *types.BlockTransactionRequest) error); ok {
 		r1 = rf(ctx, request)
 	} else {
@@ -258,13 +308,16 @@ func (_m *Client) GetNativeTransferGasLimit(ctx context.Context, toAddress strin
 	ret := _m.Called(ctx, toAddress, fromAddress, value)
 
 	var r0 uint64
+	var r1 error
+	if rf, ok := ret.Get(0).(func(context.Context, string, string, *big.Int) (uint64, error)); ok {
+		return rf(ctx, toAddress, fromAddress, value)
+	}
 	if rf, ok := ret.Get(0).(func(context.Context, string, string, *big.Int) uint64); ok {
 		r0 = rf(ctx, toAddress, fromAddress, value)
 	} else {
 		r0 = ret.Get(0).(uint64)
 	}
 
-	var r1 error
 	if rf, ok := ret.Get(1).(func(context.Context, string, string, *big.Int) error); ok {
 		r1 = rf(ctx, toAddress, fromAddress, value)
 	} else {
@@ -279,13 +332,16 @@ func (_m *Client) GetNonce(_a0 context.Context, _a1 client.Options) (uint64, err
 	ret := _m.Called(_a0, _a1)
 
 	var r0 uint64
+	var r1 error
+	if rf, ok := ret.Get(0).(func(context.Context, client.Options) (uint64, error)); ok {
+		return rf(_a0, _a1)
+	}
 	if rf, ok := ret.Get(0).(func(context.Context, client.Options) uint64); ok {
 		r0 = rf(_a0, _a1)
 	} else {
 		r0 = ret.Get(0).(uint64)
 	}
 
-	var r1 error
 	if rf, ok := ret.Get(1).(func(context.Context, client.Options) error); ok {
 		r1 = rf(_a0, _a1)
 	} else {
@@ -314,6 +370,10 @@ func (_m *Client) GetTransactionReceipt(ctx context.Context, tx *client.LoadedTr
 	ret := _m.Called(ctx, tx)
 
 	var r0 *client.RosettaTxReceipt
+	var r1 error
+	if rf, ok := ret.Get(0).(func(context.Context, *client.LoadedTransaction) (*client.RosettaTxReceipt, error)); ok {
+		return rf(ctx, tx)
+	}
 	if rf, ok := ret.Get(0).(func(context.Context, *client.LoadedTransaction) *client.RosettaTxReceipt); ok {
 		r0 = rf(ctx, tx)
 	} else {
@@ -322,7 +382,6 @@ func (_m *Client) GetTransactionReceipt(ctx context.Context, tx *client.LoadedTr
 		}
 	}
 
-	var r1 error
 	if rf, ok := ret.Get(1).(func(context.Context, *client.LoadedTransaction) error); ok {
 		r1 = rf(ctx, tx)
 	} else {
@@ -337,6 +396,10 @@ func (_m *Client) GetUncles(ctx context.Context, head *coretypes.Header, body *c
 	ret := _m.Called(ctx, head, body)
 
 	var r0 []*coretypes.Header
+	var r1 error
+	if rf, ok := ret.Get(0).(func(context.Context, *coretypes.Header, *client.RPCBlock) ([]*coretypes.Header, error)); ok {
+		return rf(ctx, head, body)
+	}
 	if rf, ok := ret.Get(0).(func(context.Context, *coretypes.Header, *client.RPCBlock) []*coretypes.Header); ok {
 		r0 = rf(ctx, head, body)
 	} else {
@@ -345,7 +408,6 @@ func (_m *Client) GetUncles(ctx context.Context, head *coretypes.Header, body *c
 		}
 	}
 
-	var r1 error
 	if rf, ok := ret.Get(1).(func(context.Context, *coretypes.Header, *client.RPCBlock) error); ok {
 		r1 = rf(ctx, head, body)
 	} else {
@@ -360,6 +422,10 @@ func (_m *Client) ParseOps(tx *client.LoadedTransaction) ([]*types.Operation, er
 	ret := _m.Called(tx)
 
 	var r0 []*types.Operation
+	var r1 error
+	if rf, ok := ret.Get(0).(func(*client.LoadedTransaction) ([]*types.Operation, error)); ok {
+		return rf(tx)
+	}
 	if rf, ok := ret.Get(0).(func(*client.LoadedTransaction) []*types.Operation); ok {
 		r0 = rf(tx)
 	} else {
@@ -368,7 +434,6 @@ func (_m *Client) ParseOps(tx *client.LoadedTransaction) ([]*types.Operation, er
 		}
 	}
 
-	var r1 error
 	if rf, ok := ret.Get(1).(func(*client.LoadedTransaction) error); ok {
 		r1 = rf(tx)
 	} else {
@@ -383,6 +448,10 @@ func (_m *Client) PopulateCrossChainTransactions(_a0 *coretypes.Block, _a1 []*cl
 	ret := _m.Called(_a0, _a1)
 
 	var r0 []*types.Transaction
+	var r1 error
+	if rf, ok := ret.Get(0).(func(*coretypes.Block, []*client.LoadedTransaction) ([]*types.Transaction, error)); ok {
+		return rf(_a0, _a1)
+	}
 	if rf, ok := ret.Get(0).(func(*coretypes.Block, []*client.LoadedTransaction) []*types.Transaction); ok {
 		r0 = rf(_a0, _a1)
 	} else {
@@ -391,7 +460,6 @@ func (_m *Client) PopulateCrossChainTransactions(_a0 *coretypes.Block, _a1 []*cl
 		}
 	}
 
-	var r1 error
 	if rf, ok := ret.Get(1).(func(*coretypes.Block, []*client.LoadedTransaction) error); ok {
 		r1 = rf(_a0, _a1)
 	} else {
@@ -406,6 +474,13 @@ func (_m *Client) Status(_a0 context.Context) (*types.BlockIdentifier, int64, *t
 	ret := _m.Called(_a0)
 
 	var r0 *types.BlockIdentifier
+	var r1 int64
+	var r2 *types.SyncStatus
+	var r3 []*types.Peer
+	var r4 error
+	if rf, ok := ret.Get(0).(func(context.Context) (*types.BlockIdentifier, int64, *types.SyncStatus, []*types.Peer, error)); ok {
+		return rf(_a0)
+	}
 	if rf, ok := ret.Get(0).(func(context.Context) *types.BlockIdentifier); ok {
 		r0 = rf(_a0)
 	} else {
@@ -414,14 +489,12 @@ func (_m *Client) Status(_a0 context.Context) (*types.BlockIdentifier, int64, *t
 		}
 	}
 
-	var r1 int64
 	if rf, ok := ret.Get(1).(func(context.Context) int64); ok {
 		r1 = rf(_a0)
 	} else {
 		r1 = ret.Get(1).(int64)
 	}
 
-	var r2 *types.SyncStatus
 	if rf, ok := ret.Get(2).(func(context.Context) *types.SyncStatus); ok {
 		r2 = rf(_a0)
 	} else {
@@ -430,7 +503,6 @@ func (_m *Client) Status(_a0 context.Context) (*types.BlockIdentifier, int64, *t
 		}
 	}
 
-	var r3 []*types.Peer
 	if rf, ok := ret.Get(3).(func(context.Context) []*types.Peer); ok {
 		r3 = rf(_a0)
 	} else {
@@ -439,7 +511,6 @@ func (_m *Client) Status(_a0 context.Context) (*types.BlockIdentifier, int64, *t
 		}
 	}
 
-	var r4 error
 	if rf, ok := ret.Get(4).(func(context.Context) error); ok {
 		r4 = rf(_a0)
 	} else {
@@ -468,6 +539,10 @@ func (_m *Client) TraceBlockByHash(_a0 context.Context, _a1 common.Hash, _a2 []c
 	ret := _m.Called(_a0, _a1, _a2)
 
 	var r0 map[string][]*client.FlatCall
+	var r1 error
+	if rf, ok := ret.Get(0).(func(context.Context, common.Hash, []client.RPCTransaction) (map[string][]*client.FlatCall, error)); ok {
+		return rf(_a0, _a1, _a2)
+	}
 	if rf, ok := ret.Get(0).(func(context.Context, common.Hash, []client.RPCTransaction) map[string][]*client.FlatCall); ok {
 		r0 = rf(_a0, _a1, _a2)
 	} else {
@@ -476,7 +551,6 @@ func (_m *Client) TraceBlockByHash(_a0 context.Context, _a1 common.Hash, _a2 []c
 		}
 	}
 
-	var r1 error
 	if rf, ok := ret.Get(1).(func(context.Context, common.Hash, []client.RPCTransaction) error); ok {
 		r1 = rf(_a0, _a1, _a2)
 	} else {
@@ -491,6 +565,10 @@ func (_m *Client) TraceReplayBlockTransactions(ctx context.Context, hsh string)
 	ret := _m.Called(ctx, hsh)
 
 	var r0 map[string][]*client.FlatCall
+	var r1 error
+	if rf, ok := ret.Get(0).(func(context.Context, string) (map[string][]*client.FlatCall, error)); ok {
+		return rf(ctx, hsh)
+	}
 	if rf, ok := ret.Get(0).(func(context.Context, string) map[string][]*client.FlatCall); ok {
 		r0 = rf(ctx, hsh)
 	} else {
@@ -499,7 +577,6 @@ func (_m *Client) TraceReplayBlockTransactions(ctx context.Context, hsh string)
 		}
 	}
 
-	var r1 error
 	if rf, ok := ret.Get(1).(func(context.Context, string) error); ok {
 		r1 = rf(ctx, hsh)
 	} else {
@@ -514,6 +591,11 @@ func (_m *Client) TraceReplayTransaction(ctx context.Context, hsh string) (json.
 	ret := _m.Called(ctx, hsh)
 
 	var r0 json.RawMessage
+	var r1 []*client.FlatCall
+	var r2 error
+	if rf, ok := ret.Get(0).(func(context.Context, string) (json.RawMessage, []*client.FlatCall, error)); ok {
+		return rf(ctx, hsh)
+	}
 	if rf, ok := ret.Get(0).(func(context.Context, string) json.RawMessage); ok {
 		r0 = rf(ctx, hsh)
 	} else {
@@ -522,7 +604,6 @@ func (_m *Client) TraceReplayTransaction(ctx context.Context, hsh string) (json.
 		}
 	}
 
-	var r1 []*client.FlatCall
 	if rf, ok := ret.Get(1).(func(context.Context, string) []*client.FlatCall); ok {
 		r1 = rf(ctx, hsh)
 	} else {
@@ -531,7 +612,6 @@ func (_m *Client) TraceReplayTransaction(ctx context.Context, hsh string) (json.
 		}
 	}
 
-	var r2 error
 	if rf, ok := ret.Get(2).(func(context.Context, string) error); ok {
 		r2 = rf(ctx, hsh)
 	} else {
@@ -546,6 +626,11 @@ func (_m *Client) TraceTransaction(ctx context.Context, hash common.Hash) (json.
 	ret := _m.Called(ctx, hash)
 
 	var r0 json.RawMessage
+	var r1 []*client.FlatCall
+	var r2 error
+	if rf, ok := ret.Get(0).(func(context.Context, common.Hash) (json.RawMessage, []*client.FlatCall, error)); ok {
+		return rf(ctx, hash)
+	}
 	if rf, ok := ret.Get(0).(func(context.Context, common.Hash) json.RawMessage); ok {
 		r0 = rf(ctx, hash)
 	} else {
@@ -554,7 +639,6 @@ func (_m *Client) TraceTransaction(ctx context.Context, hash common.Hash) (json.
 		}
 	}
 
-	var r1 []*client.FlatCall
 	if rf, ok := ret.Get(1).(func(context.Context, common.Hash) []*client.FlatCall); ok {
 		r1 = rf(ctx, hash)
 	} else {
@@ -563,7 +647,6 @@ func (_m *Client) TraceTransaction(ctx context.Context, hash common.Hash) (json.
 		}
 	}
 
-	var r2 error
 	if rf, ok := ret.Get(2).(func(context.Context, common.Hash) error); ok {
 		r2 = rf(ctx, hash)
 	} else {
@@ -572,3 +655,17 @@ func (_m *Client) TraceTransaction(ctx context.Context, hash common.Hash) (json.
 
 	return r0, r1, r2
 }
+
+// NewClient creates a new instance of Client. It also registers a testing interface on the mock and a cleanup function to assert the mocks expectations.
+// The first argument is typically a *testing.T value.
+func NewClient(t interface {
+	mock.TestingT
+	Cleanup(func())
+}) *Client {
+	mock := &Client{}
+	mock.Mock.Test(t)
+
+	t.Cleanup(func() { mock.AssertExpectations(t) })
+
+	return mock
+}
diff --git a/services/construction/types.go b/services/construction/types.go
index 17c3e96..2e4662b 100644
--- a/services/construction/types.go
+++ b/services/construction/types.go
@@ -22,6 +22,7 @@ import (
 	evmClient "github.com/coinbase/rosetta-geth-sdk/client"
 	"github.com/coinbase/rosetta-geth-sdk/configuration"
 	RosettaTypes "github.com/coinbase/rosetta-sdk-go/types"
+	Eth "github.com/ethereum/go-ethereum"
 	"github.com/ethereum/go-ethereum/common"
 	EthTypes "github.com/ethereum/go-ethereum/core/types"
 	"github.com/ethereum/go-ethereum/rpc"
@@ -181,4 +182,10 @@ type Client interface {
 	ParseOps(
 		tx *evmClient.LoadedTransaction,
 	) ([]*RosettaTypes.Operation, error)
+
+	// EstimateGas tries to estimate the gas needed to execute a specific transaction based on
+	// the current pending state of the backend blockchain. There is no guarantee that this is
+	// the true gas limit requirement as other transactions may be added or removed by miners,
+	// but it should provide a basis for setting a reasonable default.
+	EstimateGas(ctx context.Context, msg Eth.CallMsg) (uint64, error)
 }
diff --git a/services/mapper.go b/services/mapper.go
index ede8e9f..fcd14c6 100644
--- a/services/mapper.go
+++ b/services/mapper.go
@@ -130,7 +130,7 @@ func TransferOps(tx *evmClient.LoadedTransaction, startIndex int) []*RosettaType
 	return ops
 }
 
-func FeeOps(tx *evmClient.LoadedTransaction) []*RosettaTypes.Operation {
+func FeeOps(tx *evmClient.LoadedTransaction, native_currency *RosettaTypes.Currency) []*RosettaTypes.Operation {
 	var minerEarnedAmount *big.Int
 	if tx.FeeBurned == nil {
 		minerEarnedAmount = tx.FeeAmount
@@ -157,7 +157,7 @@ func FeeOps(tx *evmClient.LoadedTransaction) []*RosettaTypes.Operation {
 			Account: &RosettaTypes.AccountIdentifier{
 				Address: evmClient.MustChecksum(tx.From.String()),
 			},
-			Amount: evmClient.Amount(new(big.Int).Neg(minerEarnedAmount), sdkTypes.Currency),
+			Amount: evmClient.Amount(new(big.Int).Neg(minerEarnedAmount), native_currency),
 		},
 
 		{
@@ -174,7 +174,7 @@ func FeeOps(tx *evmClient.LoadedTransaction) []*RosettaTypes.Operation {
 			Account: &RosettaTypes.AccountIdentifier{
 				Address: evmClient.MustChecksum(feeRewarder),
 			},
-			Amount: evmClient.Amount(minerEarnedAmount, sdkTypes.Currency),
+			Amount: evmClient.Amount(minerEarnedAmount, native_currency),
 		},
 	}
 
@@ -184,12 +184,12 @@ func FeeOps(tx *evmClient.LoadedTransaction) []*RosettaTypes.Operation {
 
 	burntOp := &RosettaTypes.Operation{
 		OperationIdentifier: &RosettaTypes.OperationIdentifier{
-			Index: 0, // nolint:gomnd
+			Index: 2, // nolint:gomnd
 		},
 		Type:    sdkTypes.FeeOpType,
 		Status:  RosettaTypes.String(sdkTypes.SuccessStatus),
 		Account: evmClient.Account(tx.From),
-		Amount:  evmClient.Amount(new(big.Int).Neg(tx.FeeBurned), sdkTypes.Currency),
+		Amount:  evmClient.Amount(new(big.Int).Neg(tx.FeeBurned), native_currency),
 	}
 
 	ops = append(ops, burntOp)
@@ -203,6 +203,7 @@ func FeeOps(tx *evmClient.LoadedTransaction) []*RosettaTypes.Operation {
 func TraceOps(
 	calls []*evmClient.FlatCall,
 	startIndex int,
+	native_currency *RosettaTypes.Currency,
 ) []*RosettaTypes.Operation { // nolint: gocognit
 	var ops []*RosettaTypes.Operation
 	if len(calls) == 0 {
@@ -250,7 +251,7 @@ func TraceOps(
 				},
 				Amount: &RosettaTypes.Amount{
 					Value:    new(big.Int).Neg(trace.Value).String(),
-					Currency: sdkTypes.Currency,
+					Currency: native_currency,
 				},
 				Metadata: metadata,
 			}
@@ -311,7 +312,7 @@ func TraceOps(
 				},
 				Amount: &RosettaTypes.Amount{
 					Value:    trace.Value.String(),
-					Currency: sdkTypes.Currency,
+					Currency: native_currency,
 				},
 				Metadata: metadata,
 			}
@@ -355,7 +356,7 @@ func TraceOps(
 			},
 			Amount: &RosettaTypes.Amount{
 				Value:    new(big.Int).Neg(val).String(),
-				Currency: sdkTypes.Currency,
+				Currency: native_currency,
 			},
 		})
 	}