Abstract. Regular expressions (REs), because of their succinctness and clear syntax, are the common choice to represent regular languages. However, efficient pattern matching or word recognition depend on the size of the equivalent nondeterministic finite automata (NFA). We present the implementation of several algorithms for constructing small ε-free NFAs from REs within the FAdo system, and a comparison of regular expression measures and NFA sizes based on experimental results obtained from uniform random generated REs. For this analysis, nonredundant REs and reduced REs in star normal form were considered. 1