U.S. carriers led by United Continental Holdings are shielding their lucrative trans-Atlantic business from the worst of Europe’s economic slump, after shrinking the supply of seats to support higher fares.

Summer ticket prices to Western Europe have risen an average of 3 percent from 2011, according to Travelocity.com.

Demand for U.S.-to-Europe trips also is holding up, with ticket sales climbing 5.9 percent to 1.31 million for the peak travel months, according to data compiled by Airlines Reporting Corp.

Flights across the Atlantic are the biggest overseas market for U.S. airlines, with traffic that can roughly double in U.S. summer months from wintertime lows, data compiled by Bloomberg show.

Cutting capacity helps carriers maintain pricing power, especially with European business travel at risk from the region’s economic slowdown.

“The industry is being proactive about restructuring the amount of seats that are available for sale given the European debt crisis,” Dan McKenzie, an analyst at Rodman & Renshaw in New York, said.

Delta Air Lines, traditionally the first U.S. carrier to report operating results each month, probably will give the initial glimpse at summertime flights to Europe this week with its traffic report for June. After paring capacity, it filled 84.6 percent of seats on trans-Atlantic flights in May, up 0.9 percentage point from a year earlier, even as traffic fell.

“All indications are that Europe is holding up well, David Fintzen, an analyst at Barclays Capital in New York, said. “You’ve seen underlying demand trends get a little bit stronger over the last couple of months.”

That pattern shows up in the information from Airlines Reporting, which clears transactions for flights booked on U.S. airlines. That gives the Arlington, Va., company a look at future bookings instead of the backward snapshot provided by carriers.

While the number of tickets sold for each of the three summer months increased, the data also show challenges as airlines grapple with slowing economic growth.

Fares for both June and July bookings declined before an August increase, Airlines Reporting data showed.

Flights from the U.S. to western Europe are averaging $1,315 for May through September, up about 3 percent from the same period in 2011, Travelocity data show.

Ticket prices, pressured by competition in the past, are benefiting from industry consolidation and a growing number of global marketing alliances, said Courtney Scott, editor at Travelocity in Southlake, Texas.

Delta bought Northwest Airlines in October 2008 and was the world’s largest carrier until United Airlines combined with Continental Airlines to form United Continental in 2010.

Southwest Airlines, the biggest U.S. discount carrier, acquired AirTran Holdings in May 2011.

“We’re seeing a higher increase in airfares because of these mergers,” Scott said. “The prices are just going to just keep going up.”

Jet-fuel prices dropped 7 percent to $3.03 a gallon in May, paring a first-quarter surge, without relaxing availability of seats overall.

The drop, which means lower costs for airlines, has helped spur gains in their shares.

The Bloomberg U.S. Airlines Index of 10 carriers climbed 23 percent this year through Wednesday, with Atlanta-based Delta and United Continental among the top five performers.

United Continental, based in Chicago, will remain “disciplined” in managing capacity and won’t be affected by short-term swings in fuel prices, Chief Executive Officer Jeff Smisek told shareholders at a meeting last month.

United trimmed its schedule for July and August.