In the following video, Motley Fool energy analyst Joel South takes a question from a Fool reader, who writes: "What are your thoughts on natural gas as a transportation fuel? Can Westport Innovations (NASDAQ:WPRT) and Clean Energy Fuels (NASDAQ:CLNE) fill this niche?"

Joel South has no position in any stocks mentioned. The Motley Fool recommends Clean Energy Fuels and Westport Innovations and owns shares of Westport Innovations. Try any of our Foolish newsletter services free for 30 days. We Fools don't all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.