NEW YORK (AP) -- Drivers aren't the only ones getting stung by high-priced oil. A study released Thursday by an aviation consulting firm finds that surging fuel prices have left many of the world's airliners "economically obsolete" because they are simply too expensive to operate.

Most at risk are smaller regional jets, especially those with fewer than 50 seats, that are used to connect smaller airports to larger hubs, according to the aircraft fleet forecast by The Boyd Group in Evergreen, Colo.

More than half of the existing regional jets in service in the U.S. -- more than 900 aircraft -- will be retired over the next five to 10 years, the report said. Many won't be replaced.

For travelers, that could mean less-frequent service, fewer travel options and more time spent waiting at airports for connecting flights.

"The regional jet era is dead as a dodo," said longtime industry observer Mike Boyd, who heads the consultancy. "In most cases, a lot of the flying ... is going to go away."

Airline executives have been exploring acquisitions, additional capacity cutbacks and other initiatives to restructure the U.S. airline market in response to rising fuel costs, which now account for many carriers' biggest expense.

But the report warns that "mergers won't change the fact that existing fleets are incompatible with $110 oil prices."

Crude prices topped $110 a barrel for the first time last week but have since eased. Light, sweet crude for May delivery dropped $1.76 to $100.78 a barrel on the New York Mercantile Exchange on Thursday morning.

Meanwhile, analysts at UBS and Lehman Brothers cut their earnings estimates and lowered ratings on a number of U.S. carriers because of concerns over record-high fuel costs and a possible recession.

Jet fuel, like gasoline, has grown more expensive with crude's ascent. Last week, spot jet fuel prices jumped to a new record of $3.48 a gallon, according to the Energy Department's Energy Information Administration.

Major carriers such as AMR Corp.'s American Airlines and UAL Corp.'s United Airlines have little room to maneuver, the report suggests, because a large gap exists between the size of their inefficient regional jets and the bigger, more economical planes in their fleets.

Pulling low-mileage planes out of service means demand for more-efficient planes is likely to spike between this year and 2017, the period covered by the report. About 40 percent of the more than 14,000 planes expected to be delivered over the decade will be medium-range planes with 75 to 125 seats, the report predicts.

That is good news for Brazil's Embraer, the only aircraft maker offering a mainline model of that size, the firm noted.

"The problem is they don't have the capacity to meet demand," Boyd said. That, he added, creates a potential opening for new manufacturers in Asia or elsewhere.

Embraer, or Empresa Brasileira de Aeronautica SA, is the world's fourth-largest commercial aircraft maker, after Boeing Co., Airbus parent European Aeronautic Defence and Space Co., and Canada's Bombardier Inc. Its jets are used by JetBlue Airways Corp., ACE Aviation Holdings Inc.'s Air Canada, and some U.S. regional airlines.

The report also noted that a large backlog and delays in the introduction of Boeing's new 787 are creating a strong market for the Airbus A350. That plane, which was redesigned to better compete with the relatively fuel-efficient 787, is scheduled to enter commercial service in 2013.

It is unclear when the 787, which has been hit with a series of delays, will begin flying. The head of a major customer said this week he expects the first 787 flight won't occur until the fall, and that delivery is unlikely to begin before the end of the third quarter of 2009.

Boeing shares rose 31 cents to $73.76, while Embraer's U.S.-listed shares fell 72 cents to $38.78. Airline stocks mostly rose, with the Amex Airline Index up 2.9 percent to 26.48.