diff --git a/tests/contracts/test_contract_transact_interface.py b/tests/contracts/test_contract_transact_interface.py
index dc3d503..9b3fca7 100644
--- a/tests/contracts/test_contract_transact_interface.py
+++ b/tests/contracts/test_contract_transact_interface.py
@@ -143,4 +143,4 @@ def test_auto_gas_computation_when_transacting(web3,
     assert force_bytes(final_value) == force_bytes("ÄLÄMÖLÖ")
 
     txn = web3.eth.getTransaction(txn_hash)
-    assert txn['gas'] == gas_estimate + string_contract.gas_buffer
+    assert txn['gas'] == gas_estimate + 100000
diff --git a/tests/eth-module/test_eth_sendTransaction.py b/tests/eth-module/test_eth_sendTransaction.py
index 37636c0..71ee1c4 100644
--- a/tests/eth-module/test_eth_sendTransaction.py
+++ b/tests/eth-module/test_eth_sendTransaction.py
@@ -38,3 +38,17 @@ def test_eth_sendTransaction_with_data(web3, wait_for_transaction, MATH_CODE, MA
     contract_address = txn_receipt['contractAddress']
 
     assert force_bytes(web3.eth.getCode(contract_address)) == MATH_RUNTIME
+
+
+def test_eth_sendTransaction_auto_estimates_gas_if_not_provided(web3, wait_for_transaction, MATH_CODE, MATH_RUNTIME):
+    txn_hash = web3.eth.sendTransaction({
+        "from": web3.eth.coinbase,
+        "data": MATH_CODE,
+    })
+
+    wait_for_transaction(web3, txn_hash)
+
+    txn_receipt = web3.eth.getTransactionReceipt(txn_hash)
+    contract_address = txn_receipt['contractAddress']
+
+    assert force_bytes(web3.eth.getCode(contract_address)) == MATH_RUNTIME
diff --git a/web3/contract.py b/web3/contract.py
index de95a66..a58cf92 100644
--- a/web3/contract.py
+++ b/web3/contract.py
@@ -39,9 +39,6 @@ from web3.utils.abi import (
 from web3.utils.decorators import (
     combomethod,
 )
-from web3.utils.transactions import (
-    get_block_gas_limit,
-)
 from web3.utils.events import (
     get_event_data,
 )
@@ -78,9 +75,6 @@ class Contract(object):
     # instance level properties
     address = None
 
-    # extra gas to include when auto-computing transaction gas.
-    gas_buffer = 100000
-
     def __init__(self, abi=None, address=None, code=None, code_runtime=None, source=None):
         """Create a new smart contract proxy object.
 
@@ -246,30 +240,10 @@ class Contract(object):
 
         deploy_transaction['data'] = cls.encodeConstructorData(arguments)
 
-        if 'gas' not in deploy_transaction:
-            deploy_transaction['gas'] = cls.getBufferedGasEstimate(deploy_transaction)
-
         # TODO: handle asynchronous contract creation
         txn_hash = cls.web3.eth.sendTransaction(deploy_transaction)
         return txn_hash
 
-    @classmethod
-    def getBufferedGasEstimate(cls, transaction):
-        gas_estimate_transaction = dict(**transaction)
-
-        gas_estimate = cls.web3.eth.estimateGas(gas_estimate_transaction)
-
-        gas_limit = get_block_gas_limit(cls.web3)
-
-        if gas_estimate > gas_limit:
-            raise ValueError(
-                "Contract does not appear to be delpoyable within the "
-                "current network gas limits.  Estimated: {0}. Current gas "
-                "limit: {1}".format(gas_estimate, gas_limit)
-            )
-
-        return min(gas_limit, gas_estimate + cls.gas_buffer)
-
     #
     # ABI Helpers
     #
@@ -756,9 +730,6 @@ def transact_with_contract_function(contract=None,
         data=function_selector,
     )
 
-    if 'gas' not in transact_transaction:
-        transact_transaction['gas'] = contract.getBufferedGasEstimate(transact_transaction)
-
     txn_hash = contract.web3.eth.sendTransaction(transact_transaction)
     return txn_hash
 
diff --git a/web3/eth.py b/web3/eth.py
index 0f3a7b6..a3072b1 100644
--- a/web3/eth.py
+++ b/web3/eth.py
@@ -12,6 +12,9 @@ from web3.utils.types import (
 from web3.utils.functional import (
     apply_formatters_to_return,
 )
+from web3.utils.transactions import (
+    get_buffered_gas_estimate,
+)
 from web3.utils.filters import (
     BlockFilter,
     TransactionFilter,
@@ -204,6 +207,11 @@ class Eth(object):
 
     def sendTransaction(self, transaction):
         formatted_transaction = formatters.input_transaction_formatter(self, transaction)
+        if 'gas' not in formatted_transaction and 'data' in formatted_transaction:
+            formatted_transaction['gas'] = get_buffered_gas_estimate(
+                self.web3,
+                transaction=formatted_transaction,
+            )
 
         return self.request_manager.request_blocking(
             "eth_sendTransaction",
diff --git a/web3/utils/transactions.py b/web3/utils/transactions.py
index a747bba..4f0d5a6 100644
--- a/web3/utils/transactions.py
+++ b/web3/utils/transactions.py
@@ -17,3 +17,20 @@ def get_block_gas_limit(web3, block_identifier=None):
         block_identifier = web3.eth.blockNumber
     block = web3.eth.getBlock(block_identifier)
     return block['gasLimit']
+
+
+def get_buffered_gas_estimate(web3, transaction, gas_buffer=100000):
+    gas_estimate_transaction = dict(**transaction)
+
+    gas_estimate = web3.eth.estimateGas(gas_estimate_transaction)
+
+    gas_limit = get_block_gas_limit(web3)
+
+    if gas_estimate > gas_limit:
+        raise ValueError(
+            "Contract does not appear to be delpoyable within the "
+            "current network gas limits.  Estimated: {0}. Current gas "
+            "limit: {1}".format(gas_estimate, gas_limit)
+        )
+
+    return min(gas_limit, gas_estimate + gas_buffer)