In this paper we study the effects on the food market of the introduction of biofuels as a substitute for fossil fuel in the energy market. We consider a world economy with an oil cartel and a competitive fringe of farmers producing energy in the form of biofuels. Farmers also produce food and sell it on the world food market. We determine the resulting relationship between prices in the energy and food markets and characterize the cartel's extraction path and the price path of energy. We show that the price of food will be growing as long the oil stock is being depleted, whether population is growing or not, and that it will keep growing after the oil stock is exhausted if population is growing.