Experts predict that many Americans will see $5 gas before the end of the year.

Shocking, yes. But it's not that hard to believe when a gallon of gas has already inched above $4 in many states and tension in the Middle East continues to rise.

And while folks begin rethinking their driving habits and drillers scramble to ramp up production, two companies are sitting on the sidelines getting excited.

It's good to be the alternative
These companies have built out technology in anticipation of the day when natural gas starts to gain prominence.

Currently, natural gas is at its lowest level in a decade, and the stockpile of stored natural gas is more than 48% higher than its five-year average. Plus, the U.S. gets virtually all of its natural gas from within its own borders -- with enough supply to last more than 100 years -- or from Canada.

So it was really just a matter of time before companies dependent on gasoline prices began looking for an alternative. And that's exactly where Westport Innovations (Nasdaq: WPRT) and Cummins (NYSE: CMI) come into play.

Westport has developed fuel-injection technology that allows diesel engines to run on natural gas. It's not some pie-in-the-sky technology; countless companies are already making the transition. UPS, AT&T, Pepsi's Frito Lay, and Verizon have all rolled out clean fleets -- and hundreds more are likely to follow.

Westport has partnered with Cummins to build natural gas engines for medium-duty vehicles (like garbage trucks and buses). Through 2011, they've sold more than 30,000 natural gas engines, some of which are being used in garbage trucks in Long Island, N.Y., and Denver. Many other cities are rushing to jump on board.

And that's why these companies are excited about $5 gas
As the price of gasoline continues to rise -- and natural gas remains the cheaper alternative -- the economics change for companies that spend millions on gasoline.

It becomes cheaper in the long run to pay up front for the technology that will enable them to spend less on fuel.

Everything from trains to delivery trucks, construction vehicles, and more will eventually shift over to natural gas engines -- and both Westport and Cummins will be there with their cutting-edge technology to cash in on this revolution.

Which brings me to the investing lesson
A remarkably effective way to uncover successful investments is by seeking out companies on the cutting edge of a massive demographic shift.

A similar company riding this trend is Tesla Motors (Nasdaq: TSLA). It sells high-price luxury cars that are completely electric.

Its cars are perfect not just for the environmentalist (the cars release zero emissions), but also for the thrifty upper-middle class (the cars simply plug in to recharge). And they're selling out quicker than Tesla can make them -- meaning this is another company on the cutting edge of this behavioral shift, and its stock would be a smart choice today.

Two additional companies are similarly riding big trends, but in the food industry.

The first, Whole Foods (Nasdaq: WFM), was one of the first to move into the natural and organic foods space. Yet even with its dominant position in this market, it still only operates just over 300 stores (compared to nearly 1,700 for Safeway).

As consumers' eating habits continue to shift toward healthier options, and as Whole Foods continues to expand into new locations, its business will continue growing -- and its stock should rise.

Similarly, Chipotle Mexican Grill (NYSE: CMG) was one of the earliest movers into the fast-casual restaurant space. But that isn't its only distinguishing element; it also focuses on "whole foods" such as grass-fed beef and organic vegetables sourced from local farms when possible.

Having begun with with burritos, Chipotle is experimenting with other street-food concepts in a restaurant setting, like Asian menus. It also has a huge amount of potential growth by building out into breakfast offerings and by expanding internationally. No matter how you look at it, this company -- despite its massive historical growth -- still has good things ahead and should reward investors who buy even today.

Quite simply, both of these companies were -- and still are -- leading a cutting-edge demographic shift, which makes them such compelling buys today.

Of course, this idea isn't one that's isolated to the food or alternative energy industries; it's one that can be found in other sectors as well.

So I encourage you to look for more wide shifts in consumer behavior or sentiment and narrow down your focus to the one or two companies on the crest of these tidal waves. That is where you'll find your next big winner.

I learned this concept from one of the best investors I know
A key part of Motley Fool co-founder David Gardner's investing strategy is to seek out companies on the cutting edge of a new technology or a massive demographic shift. In fact, all of the companies I've mentioned above are companies that David has officially recommended.

For the first time ever, David will be building out a real-money portfolio based upon his favorite stocks. If you'd like to follow along as he builds it out -- or if you'd simply like to learn more information about David Gardner and his investing philosophy, drop your email address in the box below.