DALLAS (AP) — Southwest Airlines Co. earned a record fourth-quarter profit of $536 million as fuel costs fell by nearly one-third and offset lower fares and rising labor costs.

Net income nearly tripled from a year ago.

Chairman and CEO Gary Kelly said travel demand in 2016 continues to be strong but at weaker average fares.

With all the cash it is generating, the airline plans to buy back even more stock.

Its shares edged up in premarket trading.

Southwest said Thursday that profit excluding one-time items like fuel-hedging costs was 90 cents per share, matching the expectations of analysts surveyed by Zacks Investment Research and FactSet. The net income of $536 million compared with $190 million in the fourth quarter of 2014.

Revenue rose more than 7 percent to $4.98 billion, just below the FactSet analysts' forecast of $4.99 billion.

Passengers flew 11 percent more miles, which helped offset a 5 percent decline in the average one-way fare, to $149.94 from $158.06 a year earlier.

There weren't many empty seats. Even with Southwest's aggressive expansion, especially in Dallas and new international flights in Houston, the average flight was 84.1 percent full, up from 82 percent a year earlier.

Like other airlines, Southwest benefited greatly from plunging oil prices. The nation's fourth-biggest airline cut its fuel bill by $369 million, or 32 percent. Southwest expects the savings to extend into 2016. It forecast that it will spend $1.70 per gallon on fuel in the first quarter, compared with $2 a gallon in the same quarter of 2015.

Investors may turn their focus to labor costs, where Southwest reported a 19 percent increase in the fourth quarter, making salaries and benefits the airline's top expense, bigger than fuel.

Southwest said it will buy back another $500 million in stock above its previously announced plan. Buying stock makes the remaining shares more valuable.

For all of 2015, Southwest earned a record $2.18 billion, up 92 percent, on revenue of $19.8 billion. The airline's full-year fuel savings were $1.68 billion.

Southwest shares rose 46 cents to $39.76 in premarket trading about 90 minutes ahead of the market open. They have dropped nearly 9 percent since the beginning of the year, about the same as the Standard & Poor's 500 index. The stock has dropped nearly 4 percent in the last 12 months.