Atlanta-based Delta Air Lines continues to replace many of its smaller planes with larger ones and add seats to aircraft, which it says boosts its profit margins.

Delta has been retiring 50-seat regional jets and replacing them with larger, more efficient planes. It has also added more seats on planes by using slimline seats and re-engineered galleys that had been used for food service.

“We can put significantly more seats on the airplane without jeopardizing seat comfort or legroom,” said Delta chief financial officer Paul Jacobson during a presentation to investors this week. Larger planes also allow more first class seats, which generate more revenue. Overall, Delta has been able to reduce the number of airplanes in its domestic fleet by 15 percent compared with 2009 while keeping its seat capacity flat, according to Delta president Ed Bastian during an investor presentation Tuesday.

Separately, Bastian also said the strong dollar has hurt Delta’s international revenues. Delta has also been working to balance its fuel hedge portfolio after the decline in fuel costs led to huge losses on its advance fuel contracts.