In late 2008, Natural Gas Vehicles for America reported that most of the 130,000 natural gas vehicles in the country were fleet or specialty-use vehicles such as school buses, with only about 25 percent consisting of cars driven by regular motorists.

Average motorists still haven't steered sales of CNG cars into the fast lane, though the medium- to heavy-duty truck market — from UPS vans to trash compactors to tractor-trailers — has doubled in the last three years, NGVA Marketing Director Stephe Yborra said.