“The Wise Gas business model has changed and evolved since 2008,” said Greene, who owns a Ford Escape and a Chevrolet Cavalier that run on both CNG and conventional gasoline. “But we have continued to grow and develop into a multimillion-dollar business that is on the cutting edge of a fuel revolution.”

One reason: Greene said Wise Gas offers businesses and individual motorists the ability to save money on fuel costs while also making an eco-friendly business that contributes to U.S. energy independence — all factors that appeal to his customers.

Customers like Larry Hall.

Hall is the fuel manager for Cardinal Logistics, a North Carolina-based commercial trucking outfit that serves about 10 major clients in South Florida. Hall recently purchased a CNG truck to test the technology’s savings potential.

“It is a great leap of faith,” he said, “but we make it with eyes wide open and we hope it’s going to pay off down the road. It all comes back to the word entrepreneur, one who assumes the risk of doing business.”

Hall noted even incremental savings on the cost of diesel fuel can make a competitive difference in today’s market, even if it takes years to recoup the initial investment Cardinal has made in the CNG vehicle.

“There are obvious savings because CNG is plentiful and it’s easier to produce than diesel, and the cost is better,” Hall said. “So we bought a CNG truck as a test unit … to see where the savings lie. We think we’ll get our money back in a couple years.”

About 112,000 CNG vehicles are on the road in the United States — compared to some 13 million-plus worldwide, according to industry estimates. About 1,000 CNG fueling stations are in the United States, about half open to the public, the U.S. Energy Information Administration estimates.

One reason the numbers are small: Adding a CNG tank to a gasoline- or diesel-powered vehicle is expensive, costing from $4,000 for a small car to tens of thousands of dollars for a large truck.

Even so, many companies and cities are embracing CNG now. Choice Environmental Services of Fort Lauderdale is expanding its line of more than a dozen CNG garbage trucks. AT&T, Verizon Communications Inc. and Office Depot also use CNG-powered vans.

More CNG vehicles are also in the pipeline, with General Motors Co., Suzuki Motor Corp., Honda Motor Co., Ford Motor Co. and Fiat all manufacturing CNG vehicles.

Greene said all of these factors are creating a “growing market momentum” for CNG vehicles that he predicts will accelerate in years to come.

When he started his business, Greene said, he couldn’t envision how far the company would come in just four years.

“We reached out to 12 municipalities to see who was willing to stick with it and found several in South Florida,” he said, noting he was able to secure about $2 million in economic stimulus grant funding to launch Wise Gas and open its first facilities (which typically cost at least $500,000 to get up and operating).

“We jumped into this thinking we could do a good thing and make money doing it,” he said. “We had sales in excess of $2 million in 2011 and we are continuing to grow.”