Despite gains on international flights, United Airlines reports flat traffic in December

United Airlines said Friday that passenger traffic in December was nearly flat and a key revenue measure rose only slightly in the fourth quarter.

United Continental Holdings Inc. said passengers flew 16.89 billion miles last month, up 0.1 percent from December 2013. Domestic traffic fell 3.3 percent, while international travel rose 4.1 percent.

Because of additional flying, there were more empty seats. The average flight was 83.5 percent full, compared with 85.4 percent a year earlier.

The airline increased cargo-hauling by 13.8 percent in December and said it expects fourth-quarter cargo revenue of $250 million to $270 million, up from $220 million a year ago.

All the figures included United Express regional flights.

United said that for the October-December quarter, revenue for every seat flown one mile rose between 0.25 percent and 0.75 percent over last year. That is a closely watched figure that rises when airlines fill more seats or charge higher prices.

The airline said it spent $2.83 per gallon on jet fuel in the quarter. While that's cheaper than earlier in 2014, it included 25 cents per gallon for United to settle fuel-hedging contracts that lose value when oil prices fall.

Before the December numbers were released, shares of United Continental fell $1.30, or nearly 2 percent, to close at $65.34. They gained 77 percent in 2014.

Also Friday, Alaska Airlines parent Alaska Air Group Inc. said December traffic rose 9.1 percent from a year earlier. Revenue for each seat flown one mile fell about 2.5 percent in the fourth quarter compared with the same period in 2013, the company said. Shares of the company fell 97 cents to $59.73. They gained 63 percent last year after accounting for a stock split.

Virgin America Inc. reported that December traffic rose 1.7 percent from a year ago. The Richard Branson-backed airline is small, with just 5 percent of United's traffic and 32 percent of Alaska's. Virgin shares rose $1.23, or 3 percent, to $42.29. They began trading in November and have gained 84 percent since the initial public offering.