DALLAS (AP) — American Airlines, the nation’s largest carrier, doubled its fuel surcharge Thursday to $40 per round trip just days after a slightly larger increase led by United Airlines failed.

A spokesman for Fort Worth-based American confirmed that the airline raised its previous fuel surcharge from $10 one-way and $20 roundtrip.

Spokesman Tim Smith said American’s fuel costs rose nearly 30 percent in the fourth quarter of last year, and 33 cents of every dollar American takes in goes to pay for fuel.

“If fourth-quarter fuel prices had stayed the same as the year before, it is conceivable that we would have been talking about a quarterly profit in the neighborhood of $180 million instead of the loss we actually reported,” Smith said. “We expect fuel prices to remain high and volatile.”

American parent AMR Corp. reported Wednesday that it lost $69 million in the fourth quarter, its first loss since early 2006.