Agricultural commodity prices and oil prices: mutual causation

The world market price of many commodities including US corn (maize) peaked sharply in 2008. The US Energy Policy Act (2005) led to a rapid rise in demand for corn ethanol as a partial substitute for gasoline in the USA. In this paper we report analysis of weekly prices of corn, wheat, sugar and crude oil, together with monthly series derived from those and other weekly prices, for two consecutive seven year periods: 1999-2005 and 2006-2012. We find strong evidence of cointegration between prices in both series, but only weak evidence of causation. We conclude that the normal stimulus to production of agricultural commodities given by a price increase is sufficient to restore equilibrium in supply and demand within a period of about a year