At the same time, the high price of oil is fuelling demand for ethanol, which is used as both a substitute for and an additive to petrol.

ECONOMIST: Commodities

Ethanol, which is used mainly as an additive to petrol, is not a particularly good fuel: it offers only about two-thirds as much energy as petrol and can corrode pipelines and car engines.

ECONOMIST: America's biofuel muddle

MTBE, an additive mixed with petrol to reduce air pollution, had caused it to leak into water supplies.

ECONOMIST: Business this week