U.S. airlines may bump the most passengers in nine years, as business travelers resume flying following the deepest reductions in seats since World War II, Bloomberg reported.

Almost 220,000 passengers couldn’t get on flights in the first quarter of 2010 even though they had bought tickets, 25 percent more than a year earlier, U.S. Department of Transportation (DOT) data show. At that pace, so-called denied boardings in 2010 would surpass 2009’s 762,400 and reach the highest total since 2001.

“It’s more than inconvenience,” said Kevin Mitchell, chairman of the Business Travel Coalition, which represents about 300 corporate travel buyers. “There’s the risk of lost sales opportunities and lost productivity.”

The rate of involuntary bumpings jumped 37 percent from a year earlier, to 1.73 for each 10,000 passengers, according to the DOT. The full-year 2009 rate of 1.19 was a 13-year high.

The increase stems from a traffic revival at carriers led by Delta Air Lines Inc. and AMR Corp.’s American Airlines, which haven’t yet restored reductions in capacity made during the recession. Continental Airlines Inc. and Southwest Airlines Co. said their planes flew fuller than ever in May.

Pent-up demand for summer vacations means there won’t be many empty seats in the coming months, probably resulting in more bumping, said Rick Seaney, CEO of Dallas-based ticket-research firm FareCompare.com.

Airlines routinely sell more coach tickets than they have seats available, betting that not all passengers will show up. “Unless there’s a new law or something, it’s not going to change,” said George Hamlin, president of Hamlin Transportation Consultants in Fairfax, Va.

About 89 percent of first-quarter bumpings were voluntary, with travelers accepting inducements such as vouchers to switch flights.