{ IEnumerable queryResults; bool useParallel = true; var strings = new List(); for (int i = 0; i < 2500000; i++) strings.Add(i.ToString()); var stp = new Stopwatch(); stp.Start(); if (useParallel) queryResults = strings.AsParallel().Where(item => item.Contains("1")).ToList(); else queryResults = strings.Where(item => item.Contains("1")).ToList(); stp.Stop(); Console.WriteLine("useParallel: {0}\r\nTime Elapsed: {1}", useParallel, stp.ElapsedMilliseconds); }