Natural gas vehicles, at least in the U.S., haven't really been in demand for many years. The cheap gasoline (and diesel) that we have enjoyed for decades simply created a situation where there wasn't enough pain at the pump to drive any kind of demand of natural gas as a transportation fuel. However, the domestic cost of gas and diesel, largely driven by the international oil market, has risen considerably in the past half-decade, while the overall price of natural gas has stayed relatively low.

US Retail Gas Price Chart

US Retail Gas Price data by YCharts

Domestic oil consumption has continued to decline, since peaking in 2006:

US Oil Consumption Chart

US Oil Consumption data by YCharts

With this trend expected to continue as natural gas vehicles start to take market share in both commercial shipping and for private transportation, investment in production and infrastructure to support the growth in demand is ramping up. Does this create any opportunities for investors? Let's take a closer look. 

Chicken or egg? Neither
It's only been in the past few years that expensive (by American standards) gas and diesel has created any sustained interest in natural gas vehicles. Add in what is shown above -- a trend of reduced consumption of oil that is also expected to continue -- and this has led companies like Royal Dutch Shell (NYSE:RDS-A) and ExxonMobil (NYSE:XOM) to step up their involvement in natural gas production and refueling in North America. 

ExxonMobil is one of the largest companies in the world, a dominant player in oil and gas exploration, production, and sales to both consumers at retail and contract sales to fleets. One only has to look at its own website to see that natural gas is going to become a growing part of the company's future results:

For the next two decades, over half the growth in unconventional gas supply will be in North America, moving the U.S. energy mix toward a lower-carbon resource. This competitive energy supply provides a strong foundation for increasing economic output in the United States, opening up new and valuable opportunities in many regions and sectors of the U.S. economy...

ExxonMobil's domestic gas production also points at this: The company was the largest domestic producer of natural gas during the second quarter of 2013. Expect to see ExxonMobil continue to be active in this space.

Shell has been a big player in natural gas for years and is already one of the largest natural gas suppliers in the world. But the company isn't stopping at production. In April, Shell and TravelCenters of America (NYSE:TA) announced plans to open LNG refueling lanes at "at least" 100 TA and Petro stations in major shipping corridors across North America. 

This announcement followed two in March. The first announced plans for two liquefaction plants to provide LNG for heavy-duty land and marine vehicles in the Gulf Coast and Great Lakes regions. The second announced a collaboration between Shell and Volvo, which aims to "provide a complete solution to customers to help them convert to LNG as a fuel." 

It's not just big oil
Natural gas utility Integrys Energy Group (NYSE:TEG) is also getting in on the action, through its subsidiary Trillium CNG, which is betting heavily on CNG being the dominant fuel of choice for both the short-haul and long-haul trucking market. The company touts its "fast-fill' systems, which when combined with newer tank technology, significantly enhances the biggest limitation for CNG and trucking -- the very slow speed of refilling a big CNG tank. While the technology has certainly improved for both tank materials and compressor capabilities, CNG will continue to be limited in many areas by the lack of underlying natural gas infrastructure to connect with stations. 

Clean Energy Fuels (NASDAQ:CLNE), on the other hand, is the largest supplier of both CNG and LNG to the transportation market already, and is investing heavily in expanding access to both forms of natural gas. Clean Energy already operates more than 400 stations, both public and private, with the vast majority to-date CNG. Its "America's Natural Gas Highway," being built with partner Pilot/Flying J, is at nearly 80 built and ready to open, with another 70 already planned, extending what is already a very large lead ahead of the competition in this market. Private players like Blu. are also working to expand access to LNG. Currently, the company operates less than a dozen stations, with about as many more either planned or under construction -- but without offering both CNG and LNG the company's addressable market is limited. 

Final thoughts
Natural gas (both compressed and liquefied) is beginning to take a larger piece from an already shrinking domestic oil pie (sounds disgusting, doesn't it?) as consumers and businesses explore the benefits. The number of players, both large and small, is indicative of this trend continuing. Of the companies discussed, Clean Energy's clear head start, and the fact it doesn't rely on either LNG or CNG exclusively, are real advantages over its competitors, while ExxonMobil's track record of turning cash into more of it, largely due to fantastic management, make it the best of the big oil companies to own.

Jason Hall owns shares of Clean Energy Fuels. The Motley Fool recommends Clean Energy Fuels. Try any of our Foolish newsletter services free for 30 days. We Fools may not 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.