We study cointegration and causality between the real price of oil and the real price of the dollar over the 1974-2004 period. Our results suggest that a 10% rise in the oil price coincides with a 4.3% appreciation of the dollar in the long run, and that the causality runs from oil to the dollar. Through the development of a theoretical model, we then investigate possible reasons why this relationship could be reversed in the future due to the emergence of China as a major player on both the oil and the foreign exchange markets. (C) 2007 Elsevier Ltd. All rights reserved.