Delta Air Lines boosted its fourth quarter profit to $1.1 billion by adding more flights over the holiday-packed period and packing them even more full of passengers.

Lower fuel prices helped too, as Delta reported Tuesday that earnings rose 8% over a year earlier and beat analysts' expectations.

Shares jumped almost 5% before the opening bell.

U.S. airlines are enjoying a prolonged period of profitability that was long thought to be unlikely if not impossible. Delta has made money 10 years in a row after losing it eight times in the previous decade.

Delta CEO Ed Bastian says there is no reason to think the industry's good times will end anytime soon.

"I'm not worried at all," he said in an interview. "Travel is one of the things that is growing faster than most sectors of the economy."

Atlanta-based Delta gets two-thirds of its revenue from the U.S., which outperformed each of Delta's international regions in the fourth quarter. Delta grew nearly 5%, but it was able to raise average prices and still fill 85.6% of its seats in the fourth quarter and a record 86.3% for all of 2019.

"The domestic market still has quite a ways to go," Bastian said. "Airfares are still quite affordable."

Overseas was a mixed bag, however, with Delta's revenue down in Asia, partly because of weakness in China. Revenue on flights to and from Europe rose less than 1%.

A wild card for Delta and other airlines in 2020 could be the Boeing 737 Max. Some analysts believe airfares will drop when all those grounded Max jetliners are cleared to fly again — although no one knows when that will be. Delta never owned any Boeing 737 Max jetliners — unlike Southwest, American and United, which were forced to cancel thousands of flights and scramble their schedules.

Boeing "will get through the Max, they will get it back in the air," Bastian said, although faulting Boeing for building expectations that the plane's grounding, now at 10 months, would not last long, "which has made this whole issue seem like it has drug out longer and longer and longer."

In the fourth quarter, Delta reported adjusted earnings of $1.70 per share including a gain of 9 cents per share from existing a partnership with Gol in Latin America. That easily beat the $1.40 mean forecast from 18 analysts surveyed by FactSet.

Revenue rose 6% to $11.44 billion, topping the FactSet survey number by $100 million.

Labor spending rose 8% but Delta's fuel bill dropped 14%, a savings of $315 million compared with the same quarter in 2018.

Delta predicted that first-quarter revenue will rise 5% to 7% over the first quarter of 2019 and pretax margins will be unchanged.

Delta is the first major U.S. airline to report fourth-quarter results, and others are expected to post solid profits too.

Airlines were long considered to be boom-or-bust outfits that tracked the direction of the economy. Nobody can be really sure that they have broken free from the business cycle since there hasn't been a recession since the current run of prosperity began.

Delta, the most profitable U.S. carrier in recent years, just finished a year in which it earned $4.8 billion and a decade in which net income totaled about $34 million. That came after a decade marked by two recessions, an oil-price spike, and the 2001 terror attacks — Delta lost more than $25 billion from 2000 through 2009.