Larry Burns promotes natural gas as an alternative

Natural gas has a lot of potential advantages as a fuel because its simple molecular structure and gaseous form at ambient temperatures helps it burn very completely. Unlike gasoline and diesel fuel it emits virtually no unburned hydrocarbons,particulates and volatile organic compounds. It does of course produce carbon dioxide but carbon monoxide emissions are also low. Over on the GM Fast Lane blog, VP of R&D and Strategic Planning Larry Burns has a post extolling the virtues of natural gas. In the near term it is certainly viable as a direct vehicle fuel and automakers have dabbled in offering CNG vehicles over the years. None have been commercially successful in the the US market except for fleet applications although they are popular in some other markets around the world. While natural gas is relatively plentiful and inexpensive using it in compressed form has the same issue of bulk that hydrogen gas does. Nonetheless offering CNG versions of trucks and vans for commercial use could prove a better alternative right now with elevated liquid fuel prices. However, using natural gas longer term to fuel power plants to produce electricity for cars like the Volt and pure battery electrics is probably a better option. Another source of natural gas is the methane emitted from land-fill sites and dairy farms. If this gas is captured and burned to generate energy, it would actually be advantageous from a greenhouse gas standpoint. Methane has ten times the greenhouse gas effect of carbon dioxide so even the increased emissions of CO2 would be a net benefit if it displaces methane emissions.
[Source: GM Fastlane Blog]