Price discovery in crude oil and refined oil products has been extensively undertaken in organised futures markets for over a decade now. There are two dominant such markets today: the first one in the New York Mercantile Exchange; and the second in London's International Petroleum Exchange. With the demise of OPEC as the leading price setter for crude and products, NYMEX light sweet crude and Brent crude have usurped the role of benchmark grades for price setting. To date considerable work has been done to scrutinise the degree to which these two markets price efficiently, but little with regard to the way the two markets interact. Participants in these markets move with relative ease from one market to the other and usually take positions in both of them. It is of interest, therefore, to investigate the information transmission mechanism by looking at spillover effects and, perhaps, identify which market is the true price leader. This paper is a first attempt to look at such a problem in the energy market, although similar studies have been done on stock market indices. It is found that substantial spillover effects do exist when both markets are trading simultaneously, although IPE morning prices seem to be considerably affected by the close of the previous day on NYMEX. (C) 2001 Elsevier Science B.V. All rights reserved. JEL classification: C22, Q49.