Delta had predicted a gain of 7 percent to 9 percent in per-seat revenue. That's a closely watched revenue measure for airlines because it focuses on the money collected rather than the number of people who flew.
The increase in December revenue was because of the late Thanksgiving, which meant that many travelers started their trips in November but returned home in December. Revenue for November fell compared with a year earlier for the same reason.
Delta also said fuel for the month cost 3 cents less per gallon than it had predicted.
Shares of Atlanta-based Delta Air Lines Inc. rose $1.02, or 3.7 percent, to $28.71 in late morning trading.
Delta mostly kept a lid on growth last year. According to its traffic report released on Friday, traffic and flying capacity both rose by 1 percent for the full year. Domestic traffic was flat, while international traffic grew 2.6 percent.
Occupancy on jets flown by Delta and feeder airlines averaged 83.8 percent for 2013, the same as for 2012.
For December, traffic rose 6.9 percent compared with December 2012, while flying capacity rose 3.8 percent. Occupancy rose 2.5 percentage points to 85.2 percent.
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