United Airlines looked set on Tuesday to place a $10 billion-plus order for mid-sized wide-bodied jets that includes 25 A350 planes from European planemaker Airbus , industry sources said.

The order is part of a request for up to 150 airliners of various sizes from the UAL Corp

An industry source, asking not to be named, said the United order would include 25 mid-sized A350s from Airbus.

Such an order would be worth approximately $6 billion at average list prices, depending on the variant of plane chosen.

The Wall Street Journal reported earlier that United Airlines was close to placing an order for 50 wide-bodied jets split between Airbus and its U.S. rival Boeing .

Such an order would be worth roughly $10.5 billion at average list prices for the Boeing 787 Dreamliner and the Airbus 350, the next generation of lightweight composite-built jets being developed by the world's two large airliner manufacturers.

In practice, airlines negotiate discounts on such deals.

Airbus declined to comment. Boeing was not immediately available for comment.

Airbus sales chief John Leahy told Reuters last month that he expected a partial decision in coming months on the key contest to provide aircraft to the third-largest U.S. airline.

This might happen in two tranches. First, a wide-body deal for 20, 30 wide bodies and then come back six months from now and then maybe look at other aircraft, Leahy told Reuters at the Dubai Air Show.

A wide-body deal with an airline that shares common roots with Boeing and has always flown long-distance planes made by the U.S. planemaker would be a breakthrough for Airbus.

United so far only uses Airbus for its short-haul and medium-haul fleet.

Handing the rest of the deal to Boeing would also be seen as a confidence boost to the 787 Dreamliner project, coming weeks ahead of its first delayed maiden flight.

The 787 and A350 are both designed to address a promising market for roughly 200-300 passengers carried over long distances on two engines in planes built with tough, but lightweight, materials to save fuel and cut emissions.

Planemakers see a market for thousands of such aircraft once the airline industry recovers from recession.

(Reporting by Tim Hepher, editing by Marcel Michelson)