XmlSerializer deserialization time fluctuates on WCF service

XmlSerializer deserialization time fluctuates on WCF service References I\'ve been profiling the time it takes XmlSerializer to deserialize a static block of XML data into my custom MyXmlObject class, and the time seems to fluctuate quite dramatically from request to request, despite the data being exactly the same. I start timing the deserialization at the moment the XML is passed to the serializer.Deserialize() method, and stop the timing as soon as it is finished: HttpWebRequest request = (HttpWebRequest)WebRequest.Create(uri); //initialization stuff and writing to request stream. using (HttpWebResponse response = (HttpWebResponse)request.GetResponse()) { //If I run a stopwatch up to this point, I get the round trip time, //so I know that the stream has already been received at this point. using (Stream stream = response.GetResponseStream()) //In production this stream is received from a remote server. { Stopwatch stopwatch = new Stopwatch(); stopwatch.Start(); MyXmlObject obj = (MyXmlObject)serializer.Deserialize(stream); stopwatch.Stop(); } } My XmlSerializer object is defined as follows: private static readonly XmlSerializer serializer = new XmlSerializer(typeof(MyXmlObject)); My WCF web service is a Singleton that is multi-threaded. [ServiceBehavior( ConcurrencyMode = ConcurrencyMode.Multiple, InstanceContextMode = InstanceContextMode.Single)] Here are the results I got for 15 concurrent requests to deserialize a static block of XML data that is only 177,792 bytes: Static XML file of 177,792 bytes Request Execution (ms) 1 300 2 302 3 303 4 303 5 368 *High 6 303 7 302 8 242 *Low 9 243 10 244 11 245 12 242 13 243 14 883 *Outlier 15 260 As you can see it\'s somewhat consistent, but it still fluctuates by about +/-100ms On this relatively small XML file, the fluctuation is minimal, but if I feed it a much larger file (which I will be receiving more often in my WCF web service, it fluctuates much more drastically: Static XML file of 3,851,199 bytes Request Execution (ms) 1 1384 2 2402 3 1715 4 4000 *Outlier 5 1310 6 2132 7 1388 8 1654 9 1183 10 1464 11 2368 12 2752 *High 13 1094 *Low 14 1838 15 1940 So as you can see the amount of time it takes to deserialize the XML file is fluctuating much more than it did on the smaller file. I would expect it to be relatively the same (only +/- 100ms), but instead, I\'m seeing a difference of +/- 1200ms or greater. Furthermore, 2.5s is simply more time than I wish to give up for the deserialization of the XML into C# POD objects. What\'s interesting is that WCF serializes the C# POD objects into JSON in relatively no time at all when I return the data to the server. Questions Why are these fluctuations happening? What can I do to minimize these fluctuations, if anything? Is there another type of Xml deserialization that might be faster at turning an incoming Xml of this size into an hierarchy of C# POD objects? Perhaps DataContractSerializer? Doesn\'t DataContractSerializer use XmlSerializer beneath the hood? Please let me know if there is any information needed that I\'ve left out that would be useful to diagnosing this problem. Thanks.