Fill 'er up for 61 cents a gallon, change the oil about every 20,000 miles, tune 'er up at 60,000 miles and lower harmful emissions.

Sounds good, but who makes the car that goes 60,000 miles between tuneups and reduces pollutants? And where would you find such cheap fuel? The answers are: It doesn't take a specially manufactured car, and natural gas.Hoping those answers will help clean up the air and save money, Provo City signed a contract with Mountain Fuel Tuesday to convert 15 city cars to natural gas.

With natural gas costing less than half what gasoline costs for an equivalent amount of fuel, the conversion cost of about $2,000 per car pays for itself after about two years in gas savings alone. Less frequent car maintenance and longer service provide additional savings. Natural gas burns cleaner than gasoline, so it doesn't produce the carbon that wears out gasoline-powered engines.

"Natural gas vehicles can go 10,000 to 20,000 miles between oil changes. Spark plugs, points and other components last as long as 75,000 miles," according to the Mountain Fuel booklet, Natural Gas.

However, economics were not the Provo's first consideration in the conversion. Mayor Joe Jenkins said improved air quality was the major factor for the switch. Jenkins challenged the post office, Brigham Young University, Utah County and businesses with large fleets to convert their cars to the cleaner-burning natural gas.

Mountain Fuel President Nick Rose said, "We believe we have the cleanest burning fossil fuel. Natural gas vehicles is our flagship program." For the converted cars in Provo, a compressed natural gas filling station is open at 100 West and 200 South.

Cars run on natural gas produce 97 percent less carbon monoxide and 72 percent less reactive hydrocarbons. Other emissions, such as small particulates, are also less.

Besides looking for improved air quality and less cost, the city switched to natural gas because it is an alternative to petroleum products, Jenkins said. The United States has vast natural gas resources, making it a viable alternative to foreign oil.

Natural gas is also safer. Dave Blackburn, who heads up natural gas conversions for Mountain Fuel, said when people ask him if natural gas is safe, he says, "It's so safe, I bet you have it in your home."

In 430 million vehicle miles, there has not been one injury due to natural gas use in an automobile, said Blackburn.

The compressed natural gas cylinders, which take up about one-third of the trunk space in most converted cars, have withstood crash tests, gunfire and other hazards better than a standard gas tank.

Because natural gas is lighter than air, it dissipates quickly. If a severe accident ruptured the tank, the fire danger is less with natural gas than with gasoline. Spilled gasoline collects and forms a pool rather than dissipates.

Blackburn said the Provo fueling station is open 24 hours a day. A Mountain Fuel card that looks like a card for an automatic teller machine is used to pay for the compressed natural gas.

Geneva Steel President Joe Cannon is a card-carrying natural gas user. He converted his car to natural gas and plans to have several more natural gas vehicles at Geneva Steel.

Mountain Fuel has about 300 cars operating on natural gas. In order to convert a car, it must have a computer controlled fuel injection system.

Worldwide about 70,000 cars use natural gas, Blackburn said.