The U.S. economy has experienced nine recessions over the post-World War II period. Whether the causes of these recessions are primarily real or monetary has been widely debated. In this paper we examine two seemingly conflicting results regarding the primary causes of contractions in U.S. economic activity since the end of World War II. One set of results obtained by Hamilton (1983) shows that major downturns in U.S. economic activity are associated with prior exogenous increases in oil prices, while another set of results established by Romer and Romer (1989) indicate that exogenous tightening in monetary policy is the major cause of declines in industrial production and increases in …