A large number of papers published in the last decade have attempted ro show that energy markets have grown more integrated. These articles attempt to infer that various markets have become more "unified" because the correlation (in various forms) of prices between markers has increased during the last several years. This article suggests that a more appropriate modeling technique based on the theory of arbitrage as presented in Spiller and Wood (1988a and b), is better suited to answering this question. In this paper, the arbitrage technique is extended and applied to light crude oil markets in the 1990s. Arbitrage costs between markets are estimated. In addition, the hypothesis that crude oil markets have converged during this period is tested. Substantial though mixed support is gained for this hypothesis.