OWL is an ontology language developed by the W3C, and although initially developed for the Semantic Web, OWL has rapidly become a de facto standard for ontology development in general. The design of OWL was heavily influenced by research in description logics, and the specification includes a formal semantics. One of the goals of this formal approach was to provide interoperability: different OWL reasoners should provide the same results when processing the same ontologies. In this paper we present a system that allows users: (a) to test and compare OWL reasoners using an extensible library of real-life ontologies; (b) to check the ``correctness'' of the reasoners by comparing the computed class hierarchy; (c) to compare the performance of the reasoners when performing this task; and (d) to use SQL queries to analyse and present the results in any way they see fit.