A tremendous opportunity is opening up – right now – in a small niche of America's energy sector. It's a new development in a larger story we've been telling you in Growth Stock Wire for years now... The story is how, in just the past 10 years, America has gone from expecting to import natural gas to boasting the world's largest supplies. That's thanks to advances in drilling technology, which are allowing natural gas producers to find more and more of the stuff every day. The U.S. is now "the Saudi Arabia of natural gas." That's remaking the country's energy industry. And as I'll show you today, it will lead to huge gains for companies that can take advantage of it. The glut of gas supplies has led to a historic collapse in prices. Over the past six months, natural gas is down 40%. And it's not likely to soar soon... Looking at the numbers, the U.S. consumed roughly 24 trillion cubic feet (tcf) of natural gas in 2010. Based on estimates provided by the Potential Gas Committee, a nonprofit organization, the U.S. has roughly 2,170 tcf of natural gas reserves. Dividing 2,170 by 24 means the U.S. is sitting on a 90-year supply. Cheap natural gas is terrible for major producers like Chesapeake Energy and Talisman Energy. These companies recently announced production cuts. Chesapeake shares lost more than one-third of their value in 2011. It's just too difficult to make a profit with natural gas prices hovering below $2.75 per tcf. But it's great news for companies like Westport Innovations (WPRT). Westport makes engines that run on natural gas. The company has partnerships with just about every large engine manufacturer in the world. At current prices, natural gas as a transportation fuel is now 50% cheaper than regular gasoline. This fundamental shift in prices is causing some of the largest trucking fleets in the U.S. to switch from using diesel engines to ones that run on natural gas. These companies include Wal-Mart, Ryder, Coca-Cola, and Waste Management. It's just a matter of time before every heavy-duty truck in the U.S. runs on natural gas. Think about it this way... The difference in price between natural gas as a transportation fuel and diesel is about $2 per gallon. That may not seem like a lot, until you see the cost savings for a company like Wal-Mart, which has nearly 7,000 trucks. Let's say the average heavy-duty truck covers 100,000 miles annually. At five miles per gallon, that equals 20,000 gallons per year in fuel. A $2 savings results in roughly $40,000 a year per truck. That would save Wal-Mart $280 million a year on fuel costs (7,000 trucks x $40,000 in fuel savings). Trucking companies may look to convert their current diesel-engines fleet to natural gas right away, like Ryder and Coke. Others may wait five to 10 years... or until their fleets need to be replaced. Either way, unless trucking companies want to lose money, they will make the switch to natural gas. So even though Westport is sitting at its 52-week high, and my Small Stock Specialist readers are sitting on 180%-plus gains, I believe the company has more upside. You see, Westport is still a relatively small company ($2 billion market cap). That's just 10% of the market cap of global engine-maker Cummins. And Westport is expected to grow revenue by more than 50% annually for at least the next three years. This forecast is super-conservative if natural gas engines make their way into cars. Five years ago, this forecast may have sounded far-fetched. Today, the economics suggest this could happen in three to five years. Westport has signed partnerships with seven of the top 10 automotive companies, including GM, Toyota, and Ford.