diff --git a/Data/Bson.hs b/Data/Bson.hs
--- a/Data/Bson.hs
+++ b/Data/Bson.hs
@@ -41,6 +41,9 @@
 import Data.IORef
 import Data.Maybe (maybeToList, mapMaybe)
 import Control.Monad.Identity
+import qualified Text.ParserCombinators.ReadP as R
+import qualified Text.ParserCombinators.ReadPrec as R (lift, readS_to_Prec)
+import Text.Read (Read(..))
 
 getProcessID :: IO Int
 -- ^ Get the current process id.
@@ -53,6 +56,11 @@
 -- ^ Round second number to nearest multiple of first number. Eg: roundTo (1/1000) 0.12345 = 0.123
 roundTo mult n = fromIntegral (round (n / mult)) * mult
 
+showHexLen :: (Integral n) => Int -> n -> ShowS
+-- ^ showHex of n padded with leading zeros if necessary to fill d digits
+showHexLen d n = showString (replicate (d - sigDigits) '0') . showHex n
+	where sigDigits = ceiling $ logBase 16 $ fromIntegral n
+
 -- * Document
 
 type Document = [Field]
@@ -388,7 +396,13 @@
 -- ^ A BSON ObjectID is a 12-byte value consisting of a 4-byte timestamp (seconds since epoch), a 3-byte machine id, a 2-byte process id, and a 3-byte counter. Note that the timestamp and counter fields must be stored big endian unlike the rest of BSON. This is because they are compared byte-by-byte and we want to ensure a mostly increasing order.
 
 instance Show ObjectId where
-	showsPrec d (Oid x y) = showParen (d > 10) $ showString "Oid " . showHex x . showChar ' ' . showHex y
+	showsPrec _ (Oid x y) = showHexLen 8 x . showHexLen 16 y
+
+instance Read ObjectId where
+	readPrec = do
+		[(x, "")] <- readHex <$> R.lift (R.count 8 R.get)
+		y <- R.readS_to_Prec $ const readHex
+		return (Oid x y)
 
 timestamp :: ObjectId -> UTCTime
 -- ^ Time when objectId was created
diff --git a/bson.cabal b/bson.cabal
--- a/bson.cabal
+++ b/bson.cabal
@@ -1,5 +1,5 @@
 Name: bson
-Version: 0.1.4
+Version: 0.1.5
 Synopsis: BSON documents are JSON-like objects with a standard binary encoding
 Description: A BSON Document is an untyped (dynamically type-checked) record. I.e. it is a list of name-value pairs, where a Value is a single sum type with constructors for basic types (Bool, Int, Float, String, and Time), compound types (List, and (embedded) Document), and special types (Binary, Javascript, ObjectId, RegEx, and a few others).
 	.