The US, the world?s largest exporter of corn, will convert as much or more of the grain into ethanol next year than it will sell abroad, according to estimates by the Department of Agriculture.

Experts say that as petrol prices climb, farmers are diverting more of their harvests towards producing fuel rather than food or feedstock for animals. The new estimate highlights mounting competition between food and fuel that could drive up the price of food, pitting wealthy western car drivers against hungry consumers in developing countries.