Every reliable source I've read says that the NG supplies in the US have been dwindling for over 30 years. Worse, among the world reserves for untapped NG, the US ranks among the lowest. Perhaps even worse, the cost of compressing (liquefying) and shipping NG from countries with the largest reserves, Russia for example, would make it as energy-expensive as importing petroleum. And, would do nothing to reduce US dependence on foreign energy sources.
Plus, while the energy-cost, of converting existing transportation equipment to NG, is something I have yet to fully research, you can bet it won't be cheap. And that's not even considering converting airlines (the weight of the tanks alone would reduce the passenger/cargo capacity incredibly making airline travel even more expensive)... The task quickly becomes enormous and quite complex.
Wouldn't it be better, and simpler, if we just unite to make our individual lives more energy efficient? And to actively attempt to get the government to provide incentives for individuals and businesses to focus on conservation and truly alternative sources of energy?