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This is just a question to satisfy my curiosity. But to me it is interesting. I wrote this little simple benchmark. It calls 3 variants of Regexp execution in a random order a few thousand times: Basically, I use the same pattern but in different ways. Your ordinary way without any RegexOptions . Starting with .NET 2.0 these do not get cached. But should be "cached" because it is held in a pretty global scope and not reset. With RegexOptions.Compiled With a call to the static Regex.Match(pattern, input) which does get cached in .NET 2.0 Here is the code: static List<string> Strings = new List<string>(); static string pattern = ".*_([0-9]+)\\.([^\\.])$"; static Regex Rex = new Regex(pattern); static Regex RexCompiled = new Regex(pattern, RegexOptions.Compiled); static Random Rand = new Random(123); static Stopwatch S1 = new Stopwatch(); static Stopwatch S2 = new Stopwatch(); static Stopwatch S3 = new Stopwatch(); static void Main() { int k = 0; int c = 0; int c1 = 0; int c2 = 0; int c3 = 0; for (int i = 0; i < 50; i++) { Strings.Add("file_" + Rand.Next().ToString() + ".ext"); } int m = 10000; for (int j = 0; j < m; j++) { c = Rand.Next(1, 4); if (c == 1) { c1++; k = 0; S1.Start(); foreach (var item in Strings) { var m1 = Rex.Match(item); if (m1.Success) { k++; }; } S1.Stop(); } else if (c == 2) { c2++; k = 0; S2.Start(); foreach (var item in Strings) { var m2 = RexCompiled.Match(item); if (m2.Success) { k++; }; } S2.Stop(); } else if (c == 3) { c3++; k = 0; S3.Start(); foreach (var item in Strings) { var m3 = Regex.Match(item, pattern); if (m3.Success) { k++; }; }

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