The challenge could soon get trickier. Oil company BP announced Monday it has indefinitely shut down the nation's biggest oilfield after finding a pipeline leak, removing about 8 percent of U.S. oil production and stirring fears that already-high gas prices will shoot up further.

But there's good news for South Carolina: State transportation officials are finalizing a plan they hope will offset the uncertainty.

Within a few weeks, the state officials hope to begin replacing diesel fuel with a soybean biofuel product that is produced domestically. The new product will comprise only 20 percent of the fuel supply at first but will grow over time, said state transportation director Donald Tudor. It will be distributed to bus yards across the state.

"You're getting a more stable price structure," Tudor said. "It could help us manage the price fluctuations. And environmentally, it'll be very, very sound."

The transition from foreign oil is particularly important in South Carolina, the only state in the country that owns and runs its own school buses. Education officials said the bus fleet has shrunk, in part, because fuel and labor costs are up while funding from the state Legislature is down.

"We have done a much better job in the last 10 years of routing and scheduling, which allows a single bus to do a whole lot more," said Tudor. "Back then, the transportation was pretty simple. It's much more complicated now."

In South Carolina, the state is responsible for buses that take students to and from daily classes, but local districts manage activity buses used for longer trips and special events. Principals decide how to spend the travel money allotted annually to their schools.

"The choices are always tough," said Rock Hill school district spokeswoman Elaine Baker. "You not only have to have a bus, but you have to think about chaperones, different kinds of approvals, the cost per child. The gas is one more thing, and, of course, it's a big thing now."

Among the heaviest users of activity buses are high school marching bands, which travel to football games and competitions. Due largely to rising gas prices, many bands are limiting away game appearances and taking part in competitions only at nearby schools.

The band at Rock Hill High School, for example, will take its "Arabian Fantasy" show to Fort Mill, Blythewood and Olympic high schools this year, all within 45-minute drives. The band also is hosting two competitions.

"Every year, the prices have gone up," said band director Joe Gulledge, entering his 10th year at the school. "It limits us to sort of picking and choosing where we can go. We used to go to Columbia and further, but it's just costing more money. I don't foresee it going away."