ENGLEWOOD, Colo. (AP) — The governors of Colorado, Oklahoma, Pennsylvania and Wyoming are teaming up to encourage U.S. automakers to develop affordable natural-gas vehicles.

In a memorandum of understanding dated Wednesday, the governors said they intend to start replacing vehicles in their state fleets with natural-gas vehicles. Colorado alone has about 5,800 vehicles in its fleet, plus about 2,000 more within the state Department of Transportation.

The governors say their actions should help drive demand for alternative-fuel school buses, pickup trucks, vans and cars.

They say they will create a joint request for proposals for natural-gas vehicles that are comparable in price to gasoline-powered ones and hope other states will join them.

Colorado Gov. John Hickenlooper announced the agreement at the Colorado Natural Gas Vehicle Coalition workshop in the Denver suburb of Englewood.