Westport (Nasdaq: WPRT) and Clean Energy Fuels (Nasdaq: CLNE) are two of the longest shots in the natural gas space right now. As two highly speculative picks, both got nailed in the past month as broad markets tumbled and the Volatility Index (INDEX: ^VIX) spiked higher. Fortunately, the VIX fell back more than 12% today as the markets rallied. Pullbacks like this are promising signs for long-term investors and usually coincide with periods of outperformance.

But investors in these two companies got a much-needed bit of relief today, as both Westport and Clean Energy Fuels soared higher. Westport cruised 12% higher, while Clean Energy Fuels spiked 9% for the day. The biggest piece of favorable news is Volvo's recent announcement that it will introduce trucks with Westport's 13-liter natural gas engines. Volvo could be one of Westport's biggest supporters right now. The company uses the ISX12 engine produced from the joint venture between Westport and Cummins (NYSE: CMI) in its VNL demonstrator trucks and plans to have them commercially available in early 2013. At this point, what's good for Westport is generally also good for Cummins, and shares were correspondingly higher today as well.

It's not just Volvo, either. Westport has key relationships in place with rebounding automaker Ford (NYSE: F) regarding its heavy duty F-series trucks. Despite the speculative nature of Westport, relationships like these are a promising sign of the company's future potential. As Ford continues to stand out as the stronger of the two domestic automakers, it appears Westport put its chips in the right place.

As for Clean Energy Fuels, I didn't see any particular news that should have sent shares higher today and expect that the investor enthusiasm surrounding the stock has more to do with Westport's rise, as both companies are often mentioned in the same breath. Taking a step back, I like what the company is doing by biting off smaller market segments like trucking before tackling the broader transportation sector. Its relationship with Navistar is perhaps the best example. Like Westport, relationships like this are vital to long-term viability. Fortunately for investors, Clean Energy recognizes this and is executing accordingly.

As good as these natural gas stocks are, though, there is one energy stock that could be even better. In fact, it could be The Only Energy Stock You'll Ever Need. It's a well-positioned equipment provider that's poised to make investors today rich off the next energy spike. Read more about it.