diff --git a/minio-hs.cabal b/minio-hs.cabal
index c19f411..e1307cc 100644
--- a/minio-hs.cabal
+++ b/minio-hs.cabal
@@ -19,17 +19,19 @@ library
   exposed-modules:     Network.Minio
                      , Network.Minio.S3API
   other-modules:       Lib.Prelude
+                     , Network.Minio.API
                      , Network.Minio.Data
                      , Network.Minio.Data.ByteString
                      , Network.Minio.Data.Crypto
                      , Network.Minio.Data.Time
+                     , Network.Minio.PutObject
                      , Network.Minio.Sign.V4
-                     , Network.Minio.API
                      , Network.Minio.Utils
-                     , Network.Minio.XmlParser
                      , Network.Minio.XmlGenerator
+                     , Network.Minio.XmlParser
   build-depends:       base >= 4.7 && < 5
                      , protolude >= 0.1.6 && < 0.2
+                     , async
                      , bytestring
                      , case-insensitive
                      , conduit
@@ -43,6 +45,7 @@ library
                      , http-client
                      , http-conduit
                      , http-types
+                     , lifted-async
                      , lifted-base
                      , memory
                      , monad-control
@@ -60,6 +63,7 @@ library
                      , MultiParamTypeClasses
                      , MultiWayIf
                      , RankNTypes
+                     , TypeFamilies
                      , TupleSections
 
 test-suite minio-hs-test
@@ -69,6 +73,7 @@ test-suite minio-hs-test
   build-depends:       base
                      , minio-hs
                      , protolude >= 0.1.6 && < 0.2
+                     , async
                      , bytestring
                      , case-insensitive
                      , conduit
@@ -82,6 +87,7 @@ test-suite minio-hs-test
                      , http-client
                      , http-conduit
                      , http-types
+                     , lifted-async
                      , lifted-base
                      , memory
                      , monad-control
@@ -106,6 +112,7 @@ test-suite minio-hs-test
                      , MultiWayIf
                      , RankNTypes
                      , TupleSections
+                     , TypeFamilies
   other-modules:       Lib.Prelude
                      , Network.Minio
                      , Network.Minio.API
@@ -113,12 +120,13 @@ test-suite minio-hs-test
                      , Network.Minio.Data.ByteString
                      , Network.Minio.Data.Crypto
                      , Network.Minio.Data.Time
+                     , Network.Minio.PutObject
                      , Network.Minio.S3API
                      , Network.Minio.Sign.V4
-                     , Network.Minio.XmlGenerator
-                     , Network.Minio.XmlParser
                      , Network.Minio.Utils
+                     , Network.Minio.XmlGenerator
                      , Network.Minio.XmlGenerator.Test
+                     , Network.Minio.XmlParser
                      , Network.Minio.XmlParser.Test
 
 
diff --git a/src/Network/Minio.hs b/src/Network/Minio.hs
index 8422fe9..2431182 100644
--- a/src/Network/Minio.hs
+++ b/src/Network/Minio.hs
@@ -29,22 +29,24 @@ module Network.Minio
 
   , fGetObject
   , fPutObject
+  , ObjectData(..)
+  , putObject
   ) where
 
 {-
 This module exports the high-level Minio API for object storage.
 -}
 
-import qualified Control.Monad.Trans.Resource as R
+-- import qualified Control.Monad.Trans.Resource as R
 import qualified Data.Conduit as C
 import qualified Data.Conduit.Binary as CB
-import qualified System.IO as IO
 
 import           Lib.Prelude
 
 import           Network.Minio.Data
+import           Network.Minio.PutObject
 import           Network.Minio.S3API
-import           Network.Minio.Utils
+-- import           Network.Minio.Utils
 
 -- | Fetch the object and write it to the given file safely. The
 -- object is first written to a temporary file in the same directory
@@ -56,11 +58,5 @@ fGetObject bucket object fp = do
 
 -- | Upload the given file to the given object.
 fPutObject :: Bucket -> Object -> FilePath -> Minio ()
-fPutObject bucket object fp = do
-  (releaseKey, h) <- allocateReadFile fp
-
-  size <- liftIO $ IO.hFileSize h
-  putObject bucket object [] h 0 (fromIntegral size)
-
-  -- release file handle
-  R.release releaseKey
+fPutObject bucket object f = void $ putObject bucket object $
+                             ODFile f Nothing
diff --git a/src/Network/Minio/Data.hs b/src/Network/Minio/Data.hs
index 6da906b..a622766 100644
--- a/src/Network/Minio/Data.hs
+++ b/src/Network/Minio/Data.hs
@@ -133,6 +133,7 @@ getRegionFromRI ri = maybe "us-east-1" identity (riRegion ri)
 
 -- | Various validation errors
 data MErrV = MErrVSinglePUTSizeExceeded Int64
+           | MErrVPutSizeExceeded Int64
            | MErrVETagHeaderNotFound
   deriving (Show)
 
diff --git a/src/Network/Minio/PutObject.hs b/src/Network/Minio/PutObject.hs
new file mode 100644
index 0000000..3b27864
--- /dev/null
+++ b/src/Network/Minio/PutObject.hs
@@ -0,0 +1,147 @@
+module Network.Minio.PutObject
+  (
+    putObject
+  , ObjectData(..)
+  ) where
+
+
+import qualified Control.Monad.Trans.Resource as R
+import qualified Data.Conduit as C
+import qualified Data.Conduit.Binary as CB
+import qualified Data.List as List
+import qualified Data.ByteString.Lazy as LB
+
+import           Lib.Prelude
+
+import           Network.Minio.Data
+import           Network.Minio.S3API
+import           Network.Minio.Utils
+
+
+maxObjectSize :: Int64
+maxObjectSize = 5 * 1024 * 1024 * 1024 * 1024
+
+oneMiB :: Int64
+oneMiB = 1024 * 1024
+
+maxMultipartParts :: Int64
+maxMultipartParts = 10000
+
+-- | A data-type to represent the source data for an object. A
+-- file-path or a producer-conduit may be provided.
+--
+-- For files, a size may be provided - this is useful in cases when
+-- the file size cannot be automatically determined or if only some
+-- prefix of the file is desired.
+--
+-- For streams also, a size may be provided. This is useful to limit
+-- the input - if it is not provided, upload will continue until the
+-- stream ends or the object reaches `maxObjectsize` size.
+data ObjectData m = ODFile FilePath (Maybe Int64) -- ^ Takes filepath and optional size.
+                  | ODStream (C.Producer m ByteString) (Maybe Int64) -- ^ Pass size in bytes as maybe if known.
+
+-- | Put an object from ObjectData. This high-level API handles
+-- objects of all sizes, and even if the object size is unknown.
+putObject :: Bucket -> Object -> ObjectData Minio -> Minio ETag
+putObject b o (ODFile fp sizeMay) = do
+  isSeekable <- isFileSeekable fp
+
+  -- FIXME: allocateReadFile may return exceptions and shortcircuit
+  finalSizeMay <- maybe (do (rKey, h) <- allocateReadFile fp
+                            sizeE <- getFileSize h
+                            R.release rKey
+                            return $ hush $ sizeE
+                        )
+                  (return . Just) sizeMay
+
+  case finalSizeMay of
+    -- unable to get size, so assume non-seekable file and max-object size
+    Nothing -> sequentialMultipartUpload b o (Just maxObjectSize) $
+               CB.sourceFile fp
+
+    -- got file size, so check for single/multipart upload
+    Just size ->
+      if | size <= 64 * oneMiB -> do
+             (rKey, h) <- allocateReadFile fp
+             etag <- putObjectSingle b o [] h 0 size
+             R.release rKey
+             return etag
+         | size > maxObjectSize -> throwError $ MErrValidation $
+                                   MErrVPutSizeExceeded size
+         | isSeekable -> parallelMultipartUpload b o fp size
+         | otherwise -> sequentialMultipartUpload b o (Just size) $
+                        CB.sourceFile fp
+putObject b o (ODStream src sizeMay) = sequentialMultipartUpload b o sizeMay src
+
+-- | Select part sizes - the logic is that the minimum part-size will
+-- be 64MiB. TODO: write quickcheck tests.
+selectPartSizes :: Int64 -> [(PartNumber, Int64, Int64)]
+selectPartSizes size = List.zip3 [1..] partOffsets partSizes
+  where
+    partSize = max (64 * oneMiB) (size `div` maxMultipartParts)
+    (numParts, lastPartSize) = size `divMod` partSize
+    lastPart = filter (> 0) [lastPartSize]
+    partSizes = replicate (fromIntegral numParts) partSize ++ lastPart
+    partOffsets = List.scanl' (+) 0 partSizes
+
+parallelMultipartUpload :: Bucket -> Object -> FilePath -> Int64
+                        -> Minio ETag
+parallelMultipartUpload b o filePath size = do
+  let partSizeInfo = selectPartSizes size
+
+  -- get new upload id.
+  uploadId <- newMultipartUpload b o []
+
+  -- perform upload with 10 threads
+  uploadedParts <- limitedMapConcurrently 10 (uploadPart uploadId) partSizeInfo
+
+  completeMultipartUpload b o uploadId uploadedParts
+  where
+    uploadPart uploadId (partNum, offset, sz) = do
+      (rKey, h) <- allocateReadFile filePath
+      pInfo <- putObjectPart b o uploadId partNum [] $ PayloadH h offset sz
+      R.release rKey
+      return pInfo
+
+-- | Upload multipart object from conduit source sequentially without
+-- object size information.
+sequentialMultipartUpload :: Bucket -> Object -> Maybe Int64
+                          -> C.Producer Minio ByteString -> Minio ETag
+sequentialMultipartUpload b o sizeMay src = do
+  -- get new upload id.
+  uploadId <- newMultipartUpload b o []
+
+  -- upload parts in loop
+  uploadedParts <- loop uploadId rSrc partSizeInfo []
+
+  -- complete multipart upload
+  completeMultipartUpload b o uploadId uploadedParts
+  where
+    rSrc = C.newResumableSource src
+    partSizeInfo = selectPartSizes $ maybe maxObjectSize identity sizeMay
+
+    -- make a sink that consumes only `s` bytes
+    limitedSink s = CB.isolate (fromIntegral s) C.=$= CB.sinkLbs
+
+    -- FIXME: test, confirm and remove traceShowM statements
+    loop _ _ [] uploadedParts = return $ reverse uploadedParts
+    loop uid rSource ((partNum, _, size):ps) u = do
+      -- load data from resume-able source into bytestring.
+      (newSource, buf) <- rSource C.$$++ (limitedSink size)
+      traceShowM "psize: "
+      traceShowM (LB.length buf)
+      -- check if we got size bytes.
+      if LB.length buf == size
+        -- upload the full size part.
+        then do pInfo <- putObjectPart b o uid partNum [] $
+                         PayloadBS $ LB.toStrict buf
+                loop uid newSource ps (pInfo:u)
+
+        -- got a smaller part, so its the last one.
+        else do traceShowM (("Found a piece with length < than "::[Char]) ++ show size ++ " - uploading as last and quitting.")
+                finalData <- newSource C.$$+- (limitedSink size)
+                traceShowM "finalData size:"
+                traceShowM (LB.length finalData)
+                pInfo <- putObjectPart b o uid partNum [] $
+                         PayloadBS $ LB.toStrict buf
+                return $ reverse (pInfo:u)
diff --git a/src/Network/Minio/S3API.hs b/src/Network/Minio/S3API.hs
index 504a5b3..661d99a 100644
--- a/src/Network/Minio/S3API.hs
+++ b/src/Network/Minio/S3API.hs
@@ -17,12 +17,7 @@ module Network.Minio.S3API
   -- * Creating buckets and objects
   ---------------------------------
   , putBucket
-  , putObject
-
-  -- * Deletion APIs
-  --------------------------
-  , deleteBucket
-  , deleteObject
+  , putObjectSingle
 
   -- * Multipart Upload APIs
   --------------------------
@@ -31,6 +26,12 @@ module Network.Minio.S3API
   , completeMultipartUpload
   , abortMultipartUpload
   , listIncompleteUploads
+
+  -- * Deletion APIs
+  --------------------------
+  , deleteBucket
+  , deleteObject
+
   ) where
 
 import qualified Data.Conduit as C
@@ -89,21 +90,28 @@ maxSinglePutObjectSizeBytes = 5 * 1024 * 1024 * 1024
 
 -- | PUT an object into the service. This function performs a single
 -- PUT object call, and so can only transfer objects upto 5GiB.
-putObject :: Bucket -> Object -> [HT.Header] -> Handle -> Int64
-          -> Int64 -> Minio ()
-putObject bucket object headers h offset size = do
+putObjectSingle :: Bucket -> Object -> [HT.Header] -> Handle -> Int64
+                -> Int64 -> Minio ETag
+putObjectSingle bucket object headers h offset size = do
   -- check length is within single PUT object size.
   when (size > maxSinglePutObjectSizeBytes) $
     throwError $ MErrValidation $ MErrVSinglePUTSizeExceeded size
 
   -- content-length header is automatically set by library.
-  void $ executeRequest $
-    def { riMethod = HT.methodPut
-        , riBucket = Just bucket
-        , riObject = Just object
-        , riHeaders = headers
-        , riPayload = PayloadH h offset size
-        }
+  resp <- executeRequest $
+          def { riMethod = HT.methodPut
+              , riBucket = Just bucket
+              , riObject = Just object
+              , riHeaders = headers
+              , riPayload = PayloadH h offset size
+              }
+
+  let rheaders = NC.responseHeaders resp
+      etag = getETagHeader rheaders
+  maybe
+    (throwError $ MErrValidation MErrVETagHeaderNotFound)
+    return etag
+
 
 
 -- | List objects in a bucket matching prefix up to delimiter,
@@ -156,8 +164,8 @@ newMultipartUpload bucket object headers = do
 
 -- | PUT a part of an object as part of a multipart upload.
 putObjectPart :: Bucket -> Object -> UploadId -> PartNumber -> [HT.Header]
-              -> Handle -> Int64 -> Int64 -> Minio PartInfo
-putObjectPart bucket object uploadId partNumber headers h offset size = do
+              -> Payload -> Minio PartInfo
+putObjectPart bucket object uploadId partNumber headers payload = do
   resp <- executeRequest $
           def { riMethod = HT.methodPut
               , riBucket = Just bucket
@@ -166,7 +174,7 @@ putObjectPart bucket object uploadId partNumber headers h offset size = do
                                                 show partNumber),
                                  ("uploadId", Just $ encodeUtf8 uploadId)]
               , riHeaders = headers
-              , riPayload = PayloadH h offset size
+              , riPayload = payload
               }
   let rheaders = NC.responseHeaders resp
       etag = getETagHeader rheaders
diff --git a/src/Network/Minio/Utils.hs b/src/Network/Minio/Utils.hs
index 5f95410..448d241 100644
--- a/src/Network/Minio/Utils.hs
+++ b/src/Network/Minio/Utils.hs
@@ -1,6 +1,9 @@
 module Network.Minio.Utils where
 
+import qualified Control.Concurrent.Async.Lifted as A
+import qualified Control.Concurrent.QSem as Q
 import qualified Control.Exception.Lifted as ExL
+import           Control.Monad.Trans.Control (liftBaseOp_, StM)
 import qualified Control.Monad.Trans.Resource as R
 import qualified Data.ByteString.Lazy as LBS
 import qualified Data.Conduit as C
@@ -21,9 +24,21 @@ allocateReadFile fp = do
   (rk, hdlE) <- R.allocate (openReadFile fp) cleanup
   either (throwError . MErrIO) (return . (rk,)) hdlE
   where
-    openReadFile f = runExceptT $ tryIO $ IO.openBinaryFile f IO.ReadMode
+    openReadFile f = ExL.try $ IO.openBinaryFile f IO.ReadMode
     cleanup = either (const $ return ()) IO.hClose
 
+getFileSize :: (R.MonadResourceBase m, R.MonadResource m, MonadError MinioErr m)
+            => Handle -> m (Either IOException Int64)
+getFileSize h = ExL.try $ liftIO $ fromIntegral <$> IO.hFileSize h
+
+isFileSeekable :: (R.MonadResource m, MonadError MinioErr m)
+               => FilePath -> m Bool
+isFileSeekable fp = do
+  (rKey, h) <- allocateReadFile fp
+  isSeekable <- liftIO $ IO.hIsSeekable h
+  R.release rKey
+  return isSeekable
+
 lookupHeader :: HT.HeaderName -> [HT.Header] -> Maybe ByteString
 lookupHeader hdr = headMay . map snd . filter (\(h, _) -> h == hdr)
 
@@ -61,3 +76,22 @@ http req mgr = do
     lbsResp <- NC.lbsResponse resp
     throwError $ MErrService $ LBS.toStrict $ NC.responseBody lbsResp
   return resp
+
+-- like mapConcurrently but with a limited number of concurrent
+-- threads.
+limitedMapConcurrently :: forall t a (m :: * -> *) b.
+                          (MonadIO m, R.MonadBaseControl IO m,
+                           StM m a ~ StM m b)
+                       => Int -> (t -> m a) -> [t] -> m [b]
+limitedMapConcurrently count act args = do
+  qSem <- liftIO $ Q.newQSem count
+  threads <- workOn qSem args
+  mapM A.wait threads
+  where
+    workOn _ [] = return []
+    workOn qs (a:as) = liftBaseOp_
+      (bracket_ (Q.waitQSem qs) (Q.signalQSem qs)) $
+      do
+        thread <- A.async $ act a
+        others <- workOn qs as
+        return (thread : others)
diff --git a/test/Spec.hs b/test/Spec.hs
index e077462..efcab1b 100644
--- a/test/Spec.hs
+++ b/test/Spec.hs
@@ -99,7 +99,7 @@ liveServerUnitTests = testGroup "Unit tests against a live server"
       h <- liftIO $ SIO.openBinaryFile "/tmp/inputfile" SIO.ReadMode
       let mb15 = 15 * 1024 * 1024
       partInfo <- forM [1..10] $ \pnum ->
-        putObjectPart bucket object uid pnum [] h 0 mb15
+        putObjectPart bucket object uid pnum [] $ PayloadH h 0 mb15
 
       step "complete multipart"
       etag <- completeMultipartUpload bucket object uid partInfo
@@ -141,6 +141,17 @@ liveServerUnitTests = testGroup "Unit tests against a live server"
       step "list incomplete multipart uploads"
       incompleteUploads <- listIncompleteUploads bucket Nothing Nothing Nothing Nothing
       liftIO $ (length $ lurUploads incompleteUploads) @?= 10
+
+  , funTestWithBucket "multipart" "testbucket5" $ \step bucket -> do
+
+      step "upload large object"
+      -- fPutObject bucket "big" "/tmp/large"
+      -- putObject bucket "big" ("/dev/zero")
+      etag <- putObject bucket "big" (ODFile "/dev/zero" $ Just $ 1024*1024*100)
+      traceShowM etag
+
+      step "cleanup"
+      deleteObject bucket "big"
   ]
 
 unitTests :: TestTree