Delta Air Lines, Inc. (DAL)

Delta Air Lines earns less from carriage than from premium cabins and its loyalty programme.

Air travel is a business of nearly fixed costs: the aircraft flies on schedule regardless of load. Profit is therefore acutely sensitive to occupancy and cabin mix: premium seats supply a disproportionate share of revenue on the same flight.

The second pillar is the co-branded card agreement: the issuing bank buys miles to award cardholders and pays hundreds of millions annually for them. That income barely depends on whether people fly and makes the company steadier than its competitors. Risks: fuel prices, unions and travel demand. The carrier bets on premium cabins and big-city hubs, where the passenger pays for the schedule rather than for the lowest fare. Delta pays a dividend.