General Motors intends to make its full-size sport utility vehicles able to burn ethanol-based fuel. Starting with the 2002 model year, its full-size SUV models that use the 5.3 litre V8 engine -- the Chevrolet Suburban and Tahoe and the GMC Yukon and Yukon XL -- will be built to run using a fuel mix of up to 85 percent ethanol, which burns cleaner than other fuels. The same modifications will be made to the Chevrolet Avalanche, a four-door pickup with SUV traits, in the 2003 model year. Combined with the ethanol-ready compact pickups GM already sells, the company said it would build one million ethanol-ready trucks by 2003.

Under EPA rules, if an automaker sells enough ethanol-ready vehicles, it can improve its average fuel economy up to 1.2 miles per gallon -- even if those vehicles never burn ethanol fuel. That can offset sales of other large, and less frugal trucks and SUVs that also bring large profits. In recent years, the truck market in the US has soared and US makers have enjoyed large margins. The vehicles themselves have got even larger.

A lack of ethanol fuels has not stopped automakers from adding ethanol-capable vehicles to their fleet, in part because of U.S. Environmental Protection Agency rules that give them credits toward corporate fuel economy standards. Ford Motor Co. sells Taurus sedans and Ranger pickups that are ethanol-ready; all Chrysler and Dodge minivans with a 3.3 litre V6 engine also can burn ethanol fuel. About 850,000 of those vehicles were built in 1999.

A number of observers claim that the vehicle makers are paying lip-service to green ideals and that the real reason for the development of these vehicles is simply to impact average fleet fuel economy. Companies that fall below official EPA fuel economy thresholds - which apply across the fleet - can face large fines.