Some uses of specialized reactors include providing heating in extremely cold climates and trying to convert coal into clean-burning gas.

Power plants started moving toward clean-burning natural gas.

Demand looks set to increase steadily at about 1.4% a year, as clean-burning gas replaces oil and coal.

Electric utilities that now use coal-fired plants are expected to move toward clean-burning gas to comply with the tougher air pollution standards.

But those supplies are tightening just as the demand for clean-burning gas is soaring.

Despite current capacity and price problems, clean-burning natural gas should be recognized as America's best source of energy for supplying electricity in the future.

Bill Kerbel, a certified industrial hygienist for Atlantic Environmental, an environmental consulting firm in Dover, N.J., said that even clean-burning natural gas can cause problems.

As for eliminating the diesel soot, the City Bus Authority could accelerate the conversion of the bus fleet to clean-burning natural gas.

In its literature, American National Power writes that the project would use "clean-burning natural gas, highly efficient electricity generating technology and cutting-edge pollution-control and water-minimization equipment.

Mr. Horton shares the view of many other industry executives that for both energy-supply and environmental reasons, clean-burning natural gas is about to come into its own.