There was an unmistakable shift in tone in the airline industry this week as the nation’s top carriers all reported record earnings because of lower fuel prices and strong demand for domestic air travel.

The airlines kept their planes full as they reaped the benefits of their yearslong drive to consolidate the industry into fewer, bigger carriers. The performance was particularly striking because the first quarter is traditionally the weakest of the year.

“We are pleased to report record first-quarter profits, exceeding the prior record set just last year,” said Doug Parker, the chairman and chief executive of American Airlines.

There was a similar theme at United Airlines, Delta Air Lines and Southwest Airlines in the last few days.