US aerospace giant Boeing has won a massive contract to supply aerial refuelling tankers to the Air Force, defeating European rival EADS in a long-running contest.

Announcing the first part of $30-billion-plus contract, the Pentagon said: “Boeing was a clear winner.”

The verdict capped a nearly 10-year attempt by the Air Force to begin to replace an aging Boeing-built fleet of tankers dating back to the 1950s. The planes, effectively flying gasoline stations, give the Air Force its global reach.

As a first step, Boeing is tasked with delivering 18 aircraft by 2017, but the contract is expected to grow to 179 tanker planes.

The decision was an upset, with most experts predicting Boeing’s European rival EADS would land the victory.

Air Force Secretary Michael Donley said both firms met 372 mandatory requirements, but because there was a more than one per cent price difference between the two companies the non-mandatory aspects were not taken into account. The lower-priced Boeing offer will offer taxpayer savings, he added.

The Air Force-led selection effort included experts from the larger Defence Department community, including the office of the Defence Secretary Robert Gates and independent review teams during each step of the process, the Pentagon said.

Facing the prospect of a procedural challenge, Mr Donley emphasized that the decision was careful and thorough.

“This isn’t about opinions, it’s about the integrity of the source selection process,” Mr Donley said.

“We hope that all parties, recognising the thorough process and intense multiple levels of review that have gone into this source selection, will respect the decision and allow this important procurement to proceed unimpeded.”

“The war fighter deserves nothing less.”