From January through June, retail gas stations experienced their best six-month period for gross margins this century, according to industry experts.

A mix of steady demand at the pump along with "stumbling wholesale prices" means gas station owners are seeing one of their best years in years, said retail fuel analyst Fred Rozell with Oil Price Information Service, a trade publication in Gaithersburg.

The company's report was based on surveys of more than 110,000 service stations, supermarkets and big-box retailers that sell fuel.

Gross gasoline margins averaged 16.9 cents per gallon in the first half of 2010, a hefty increase from 10.3 cents a year earlier.

Historically, the first six months of a year are slower for retail gas stations, Rozell said.

For years, station owners have had to consolidate, own several stations and add fare such as hot food and sandwiches to turn a profit, said Paul Fiore, director of government affairs for the Washington, D.C., Maryland, Delaware Service Station and Automotive Repair Association in Bowie.

One of the secrets of the service station business is how much they rely on food and drink sales, Fiore said.

Gross margins on gasoline sales often are so thin they do not cover credit card fees, rent and other expenses, Fiore said. An estimated 90 percent of gasoline purchases are with credit cards, which force stations to pay significant fees.

Serving food at service stations is a trend that goes back to the 1970s, pushed by oil companies that wanted service stations to get away from repairs because they took up more space on the parking lot, Fiore said.

Food and beverage sales offered higher profit margins because the service stations were selling not just food, but convenience to the motorists, Fiore said.

About 60 percent to 70 percent of the service stations in the region are convenience stores.

Even at those stations, 80 percent to 90 percent of the total sales come from gasoline, but food and drink sales bulk up the bottom line, Fiore said.

Even with healthier gross margins on gasoline this year, service station owners are not likely to turn off their cooking grills, because the oil market is so volatile, Fiore said.

"It's so fickle, volatile and fungible," Fiore said. "You never know what the next crisis will be. Just when you think you have it figured out, everything changes."

When wholesale gasoline prices increase due to rising oil prices, service station owners often are slow to follow suit, in an effort to remain competitive, Rozell said. If gas prices rise too high, as they did in 2008, motorists stop driving and instead take public transportation or cut out leisurely trips, driving down demand.