Consumers, manufacturers and fuel suppliers so far haven't shown much interest in natural gas-powered cars, even though the United States has record supplies of the fuel.

But there are signs of change.

Clean Energy Corp. is expanding natural gas refueling to 150 U.S. truck stops — though the emphasis is on tractor-trailer rigs. But Honda is expanding marketing of its compressed natural gas car to more states this model year, trying to double annual sales to about 2,000 per year.

So far, natural gas vehicles are mostly in fleets of buses, taxis and garbage haulers that have a close-by fuel source. Most private owners rely on a costly home refueler.

Backers hope that Congress approves tax credits for natural gas vehicle purchases.