Fallin estimated Oklahoma could save up to $20,000 in net fuel costs over the life of a vehicle by switching to natural gas over gasoline or diesel.
Oklahoma typically has about 11,000 vehicles in its fleet, she said. Nearly 40 percent of the vehicles in the state's current fleet have more than 100,000 miles on them.
Fallin said the state buys as many as 700 new vehicles a year, so she wants to begin moving to CNG to save money and increase demand for natural gas.
The resource is abundant in Oklahoma, which is the nation's fourth-largest producer of natural gas.
Hickenlooper said natural gas is cleaner and cheaper than oil, as evidenced by studies that show increased natural gas use has lowered carbon dioxide emissions in the U.S. to levels not seen in 50 years.
He also said the demand shown by state purchasing agents will lead to more CNG fueling stations being built around the country.
Oklahoma has more than 63 public fueling stations, the most per capita of any state in the country, Fallin said.
Colorado has 28 fueling stations, but Hickenlooper said they are located along major interstates.
At a glance
Savings on CNG vehicle bids
States interested in buying compressed natural gas vehicles have received bids for several different cars, trucks and vans. Lower prices are expected to make it more economical for states to switch to CNG.