Southwest Airlines, the Dallas-based U.S. budget air carrier that is the only U.S. airline to show consistent profits since the World Trade Center attacks of 2001, reported first-quarter net earnings of $76 million, up from $26 million in the same period last year.

The Thursday report indicated that profits were aided by the airline’s purchase of fuel at prefixed prices, which saved them $155 million in the quarter.

The report warned, however, that second-quarter fuel prices are likely to be somewhat higher than in the first quarter and that second-quarter passenger numbers will probably be down from last year’s numbers because of an early Easter break this year.

The airline also said it had increased available seats by adding seven new aircraft to its fleet. Southwest is the first company in the U.S. airline sector to report first-quarter earnings.

It is expected to be the only one to report profits. The nine largest U.S. air carriers are expected to report losses totaling at least $2 billion.