I just thought id mention that assuming you are talking about regexes of the form /^(LIST|OF|LITERALS)/ (ie no regex special characters involved and left anchored at the start of the string) then once you get over a small handful of words (last time i checked it was around 50 or so) you can actually outperform perls regex engine with a pure perl trie. Perl really doesnt handle this type of pattern very well currently, and as a pet project im working on creating two new regops, TRIE and DFA which will basically do all of this type of optimization automatically. (Which will have the disadvantage that it will make regexs like your optimized one actually perform worse than a straight list of options.) Incidentally you will probably find that if you omit the class logic the regex will run faster. As someone else mentioned already, classes disable a lot of optimizations that the engine can do.