Pennsylvania state governor Edward Rendell wants to use part of a $US260m windfall to double rebates for hybrid cars to $1,000 but Colorado's rebate of as much as $4,713 will still be one of the nation's richest, according to Reuters, citing the website HybridCars.com.

The report said more than half of US states offer motorists incentives for buying hybrid cars, whose fuel economy vastly surpasses that offered by cars with conventional engines, according to the Denver-based National Conference of State Legislatures.

Reuters added that the US government, eager to cut the nation's dependence on crude oil imports, offers tax credits ranging from $1,550 to $3,150, depending on the make and model of the hybrid car, according to an IRS spokesman.

The federal tax agency's list, which is not yet complete, appears on an Inland Revenue Service website.

Kate Burke, an analyst with the National Conference of State Legislatures, told Reuters some states offer the incentives to help them meet air quality standards.

Pennsylvania's Democratic governor, who is running for re-election, has proposed the richer hybrid car rebates as part of his plan for spending a $260m surplus, according to a statement cited in the report.

"With current fuel costs and our nation's dependence on foreign oil, the governor is keenly focused on encouraging alternate energy choices like the purchase of hybrid cars," Rendell spokeswoman Kate Philips told the news agency.

Reuters, citing the hybrid car website, noted that a number of states also offer hybrid motorists another break that is especially attractive to solo commuters -- the freedom to use high occupancy vehicle (HOV) lanes without carrying passengers.

This has led to complaints in some areas that hybrid owners are crowding HOV lanes - and driving too slowly.

Corn-rich Illinois gives motorists rebates of as much as $4,000 for switching a vehicle to burn an alternate fuel and New Haven, Connecticut, residents with hybrid cars can park for free - if they register the vehicles, according to the hybrid car website, Reuters added.

Incentives are scare for hybrid owners here in the UK, according to Toyota GB spokesman David Crouch. He said that, currently, hybrids are exempt from London's £8 a day Monday-to-Friday congestion charge.

The UK government's Powershift scheme, which offered rebates to buyers of alternative fuel and hybrid vehicles was phased out about 18 months ago when the allocated funding ran out but there has been talk that the scheme may be revived in some form.

Additional reporting: Graeme Roberts