diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,6 +1,10 @@
 # Changelog
 All notable changes to this project will be documented in this file.
 
+## [0.8.2.0] 2018-11-07
+### Changed
+- Gas estimation runs when gas limit is not set before
+
 ## [0.8.1.0] 2018-10-29
 ### Added
 - Support vinyl-0.10 in `MultiFilter` module
@@ -15,6 +19,7 @@
 - Experimental support for solidity compiler (disabled by default) 
 - Support for Ethereum mainnet ENS resolver
 - Contract typeclass with api/bytecode getters
+- Gas estimation for sending transactions
 - Contract typeclass TH generator
 - Function for creating contracts
 - Event single/multi filters
diff --git a/src/Network/Ethereum/Account/Default.hs b/src/Network/Ethereum/Account/Default.hs
--- a/src/Network/Ethereum/Account/Default.hs
+++ b/src/Network/Ethereum/Account/Default.hs
@@ -53,8 +53,11 @@
                 params = c { callData = Just $ BA.convert dat
                            , callFrom = listToMaybe accounts }
 
-            gasLimit <- Eth.estimateGas params
-            let params' = params { callGas = Just gasLimit }
+            params' <- case callGas params of
+                Just _  -> return params
+                Nothing -> do
+                    gasLimit <- Eth.estimateGas params
+                    return $ params { callGas = Just gasLimit }
 
             getReceipt =<< Eth.sendTransaction params'
 
diff --git a/src/Network/Ethereum/Account/Internal.hs b/src/Network/Ethereum/Account/Internal.hs
--- a/src/Network/Ethereum/Account/Internal.hs
+++ b/src/Network/Ethereum/Account/Internal.hs
@@ -63,12 +63,12 @@
 value = lens (fromWei . _value) $ \a b -> a { _value = toWei b }
 
 -- | Transaction gas limit lens
-gasLimit :: Lens' (CallParam p) (Maybe Integer)
-gasLimit = lens _gasLimit $ \a b -> a { _gasLimit = b }
+gasLimit :: Lens' (CallParam p) Integer
+gasLimit = lens (fromMaybe def . _gasLimit) $ \a b -> a { _gasLimit = Just b }
 
 -- | Transaction gas price lens
-gasPrice :: Unit gasprice => Lens' (CallParam p) (Maybe gasprice)
-gasPrice = lens (fmap fromWei . _gasPrice) $ \a b -> a { _gasPrice = toWei <$> b }
+gasPrice :: Unit gasprice => Lens' (CallParam p) gasprice
+gasPrice = lens (fromWei . fromMaybe def . _gasPrice) $ \a b -> a { _gasPrice = Just (toWei b) }
 
 -- | Call execution block lens
 block :: Lens' (CallParam p) DefaultBlock
diff --git a/src/Network/Ethereum/Account/Personal.hs b/src/Network/Ethereum/Account/Personal.hs
--- a/src/Network/Ethereum/Account/Personal.hs
+++ b/src/Network/Ethereum/Account/Personal.hs
@@ -63,8 +63,11 @@
                 params = c { callFrom = Just $ personalAddress _account
                            , callData = Just $ BA.convert dat }
 
-            gasLimit <- Eth.estimateGas params
-            let params' = params { callGas = Just gasLimit }
+            params' <- case callGas params of
+                Just _  -> return params
+                Nothing -> do
+                    gasLimit <- Eth.estimateGas params
+                    return $ params { callGas = Just gasLimit }
 
             getReceipt =<< Personal.sendTransaction params' (personalPassphrase _account)
 
diff --git a/src/Network/Ethereum/Account/PrivateKey.hs b/src/Network/Ethereum/Account/PrivateKey.hs
--- a/src/Network/Ethereum/Account/PrivateKey.hs
+++ b/src/Network/Ethereum/Account/PrivateKey.hs
@@ -75,8 +75,11 @@
                        , callNonce = Just nonce
                        , callData  = Just $ convert dat }
 
-        gasLimit <- lift $ Eth.estimateGas params
-        let params' = params { callGas = Just gasLimit }
+        params' <- case callGas params of
+            Just _  -> return params
+            Nothing -> do
+                gasLimit <- lift $ Eth.estimateGas params
+                return $ params { callGas = Just gasLimit }
 
         let signed = signTransaction params' (privateKeyChain _account) (privateKey _account)
         lift $ getReceipt =<< Eth.sendRawTransaction signed
diff --git a/test/Network/Ethereum/Web3/Test/SimpleStorageSpec.hs b/test/Network/Ethereum/Web3/Test/SimpleStorageSpec.hs
--- a/test/Network/Ethereum/Web3/Test/SimpleStorageSpec.hs
+++ b/test/Network/Ethereum/Web3/Test/SimpleStorageSpec.hs
@@ -8,6 +8,7 @@
 {-# LANGUAGE NamedFieldPuns        #-}
 {-# LANGUAGE OverloadedStrings     #-}
 {-# LANGUAGE QuasiQuotes           #-}
+{-# LANGUAGE RecordWildCards       #-}
 {-# LANGUAGE ScopedTypeVariables   #-}
 {-# LANGUAGE TemplateHaskell       #-}
 
@@ -34,6 +35,7 @@
 import           Data.Default                     (def)
 import           Data.List                        (sort)
 import           Data.Monoid                      ((<>))
+import           Lens.Micro                       ((.~))
 import           Test.Hspec
 
 import qualified Network.Ethereum.Api.Eth         as Eth
@@ -77,6 +79,16 @@
 
         v <- contract storage count
         v `shouldBe` theValue
+
+    it "can set transaction gas limit" $ \storage -> do
+        TxReceipt{..} <- contract storage $ withParam (gasLimit .~ 500000) $ setCount theValue
+        Just Transaction{..} <- web3 $ Eth.getTransactionByHash receiptTransactionHash
+        txGas `shouldBe` 500000
+
+    it "can estimate transaction gas limit" $ \storage -> do
+        TxReceipt{..} <- contract storage $ setCount theValue
+        Just Transaction{..} <- web3 $ Eth.getTransactionByHash receiptTransactionHash
+        txGas `shouldBe` 42822
 
 events :: SpecWith Address
 events = do
diff --git a/web3.cabal b/web3.cabal
--- a/web3.cabal
+++ b/web3.cabal
@@ -1,6 +1,6 @@
 cabal-version: 1.12
 name: web3
-version: 0.8.1.0
+version: 0.8.2.0
 license: BSD3
 license-file: LICENSE
 copyright: (c) Alexander Krupenkin 2016