Now Zwygart is like thousands of other convenience store owners across the country who sell 80 percent of the nation's gasoline: trying to keep afloat in an uncertain economy with gas prices hovering around $4 a gallon. Exact numbers are hard to come by, but dozens in Kansas may have gone out of business over the past year.

"People have slowed their buying habits. We're still selling a decent volume, but not anything like it was when it was selling for $2.90 or $3," Zwygart said. "People are buying less inside. They don't have the extra money to spend."

Zwygart's store, along Kansas 4 about 10 miles northeast of Topeka, is one of about 1,300 convenience stories in the state. According to the National Association of Convenience Stores in Alexandria, Va., the U.S. has more than 146,000 such stores -- and 56 percent of them are owned by one-store operators, also known as mom-and-pop shops.

"If you have a reliance on gas to drive your profits, you are really hurting right now and that is not just in Kansas, that is everywhere," said Jeff Lenard, spokesman for the association. "Customer loyalty now more than ever is based on the price of gasoline."

Lenard said the national average for gasoline is $4.09 and the average markup is 15 cents. He said credit-card fees pretty much wipe out the markup.