In April, Westport announced a deal with Delphi Automotive Systems to supply its HD natural gas fuel injectors to the global auto supplier spun off from General Motors last year. It's the Westport patented technology for the heavy duty truck market that sets it apart from peers in the natural gas vehicle stock space, according to analysts who cover the sector. And it's important to remember that Westport's technology for heavy duty trucks is more proprietary than other natural gas conversion kits, from players like Clean Energy Fuels and Italian company Landi Renzo ( LR), said Shawn Severson, analyst at ThinkEquity. "These companies don't compete with Westport in heavy duty trucks. Westport has that game wrapped up," the ThinkEquity analyst said. Nevertheless, the critical question is, When this game that the analyst refers to will actually begin? The natural gas vehicle stocks received a big -- albeit "iffy" -- endorsement, when the climate bill recently introduced by the Senate included a provision from the T. Boone Pickens-supported Natural Gas Act to double the size of the current federal subsidy for trucking fleet operators, including the long-haul truckers and shipping companies, to purchase natural gas powered vehicles. Stocks like Clean Energy Fuels spiked on the introduction of the climate bill. Yet given the uncertain fate of the climate bill -- some analysts believe it may never see the light of "legislative passage" day in 2010 -- these natural gas vehicle stocks remain extremely volatile.