(FORTUNE Small Business Magazine) -- In crisis lies opportunity. That's the theme of this year's FSB 100, our sixth annual ranking of the fastest-growing small public companies, measured by revenue and earnings-per-share growth and stock performance over the past three years. While drivers curse $3-a-gallon gas and military families watch footage of Iraq and Afghanistan on the evening news with prayers for safety, nimble small businesses stepped in with innovative solutions - and profited accordingly.

Oil and natural gas firms represented 13 of the 100 companies (up from nine in 2005), including eight of the top 25. "Crude oil is a world market," explains Nicholas Cacchione, co-director of research at John Herold, an independent oil and gas industry research firm in Norwalk, Conn. "If something happens anywhere in the world that affects the price of oil, it affects the small American oilman too."

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CREDO Petroleum (No. 23) is one of the companies benefiting from the price hike. Its patented device, Calliope, uses pressure differentials to extract gas from wells that others might give up on. "As a natural gas well gets older, it's like a human being - fluid builds up and suppresses the flow of gas," explains CREDO (Charts) CEO James Huffman, 59. While other technologies can remove the unwanted liquid down to 8,000 feet, Calliope has gone as deep as 18,000.

No discussion of the year's chaos would be complete without a mention of military actions around the globe and continued investment in defense. Across industry lines, at least a dozen FSB 100 companies do some business with the government, most with military products or technology.

EFJ (Charts) (No. 6), based in Irving, Texas, developed a two-way radio that can be used by first responders from federal, state, and local agencies. (To avoid the confusion seen among responders to the 9/11 attacks, new federal rules require that the communications among such agencies be integrated.)

It also designed an encryption chip that scrambles radio signals to prevent eavesdropping; it is used by the military in Iraq and Afghanistan. "There's no question that most of our growth in the last three years has been because of our opportunities around the world," says EFJ CEO Michael Jalbert, 60.

About 29% of the company's sales come from the Department of Defense. Similarly, Innovative Solutions & Support (Charts) (No. 24) retrofits military and commercial planes with new display panels that more accurately measure the distance between planes.

Compared with bombs in Fallujah, health care is a more slowly simmering woe. But according to the 2000 U.S. Census, the 45- to 64-year-old demographic is predicted to increase 35% by 2015. Aging boomers alone have made health care an ongoing mainstay of the list.

This year that trend continues with companies such as top-ranked LCA-Vision (Charts), based in Cincinnati. The company's chain of 52 clinics in the U.S. performed Lasik surgery on some 71,000 patients in 2005. "We successfully married health-care services and a passion for patient care with retail," says acting CEO Craig Joffe, 33.

Retail may be what sets the company's LasikPlus-branded centers apart. LCA-Vision chooses locations near shopping centers or highway on-ramps for maximum visibility--directions to its suburban Portland, Ore., center end with "... on the 2nd floor above the Container Store"--and by calling itself a "value-priced provider," with an average price of $1,375 per eye in the first quarter of 2006.

Not that a No. 1 spot and a hot niche are enough to sustain growth. Last year's No. 1 company, Taser (Charts), failed to make the list in 2006. While homeland security remains a spending priority, questions regarding the safety of Taser's product and the ensuing negative publicity caused revenues to drop by nearly 30% and earnings by more than 90%. Its stock opened 2005 at nearly $30 a share, but had fallen to $9.27 by June.

As bargain shoppers and economists alike try to divine the next boom or bust, our list provides one unscientific indicator: The first debt collection agency appeared on the FSB 100 in 2006. No. 69 Portfolio Recovery Associates (Charts) buys debt from lenders, seeking out the worst of the worst--situations in which even other collection agencies have thrown up their hands.

"Americans are continuing to borrow and spend, so there is just a lot of debt out there," says CEO Steven Fredrickson, 46. The company's key weapon: actually being nice. We can't blame the guy for his industry. After all, one borrower's loss can be an entrepreneur's gain.

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