Airbus unveiled orders worth a potential $6.35 billion on Thursday but its success was set to be dwarfed later in the day by a huge United Airlines deal for Boeing aircraft. European plane manufacturer Airbus announced at the Farnborough airshow near London that Russian airline UTair had placed a firm order for 20 of its single-aisle A321 passenger jets worth $2.0 billion at list prices. Latin American group Synergy Aerospace meanwhile firmed up a provisional order for nine long-haul Airbus A330 aircraft worth $1.9 billion. Irish leasing company Avolon earlier committed to buy 15 of its future single-aisle A320neo jets worth $1.45 billion and Lebanese airline MEA proposed to buy 10 of the planes for $1.0 billion. On Wednesday, Avolon had committed to buy 25 737 MAX jets, with Boeing saying that deal was worth $2.3 billion. In total, the Airbus orders Thursday were worth $6.35 billion (5.2 billion euros) but aircraft buyers typically receive big discounts on the list prices. The flurry of Airbus contracts was set to be dwarfed later Thursday by a single firm order from US carrier United Airlines for a reported 100 single-aisle 737 Boeing planes, including many of its future MAX jet, designed to compete directly with the A320neo. \"Boeing should announce a big order of 737s by United,\" a source close to the deal told AFP. US planemaker Boeing said it and United Airlines were to make a \"major announcement\" at 1400 GMT. The Seattle Times reported that the deal was for \"a firm order for 100 of Boeing\'s single-aisle 737s, most of them the forthcoming model with new fuel-efficient engines, the 737 MAX.\" It said the deal could be worth up to $10 billion at list prices and include an option for the carrier to purchase 100 more planes, the newspaper added. Airbus said on Thursday that it had won firm orders and commitments at the Farnborough airshow that started on Monday worth a combined $16.9 billion -- a figure that was set to be easily beaten by Boeing\'s total. However, Airbus came out on top at last year\'s Paris airshow thanks to big orders for its neo series which goes head-to-head in the short-haul passenger plane market with Boeing\'s 737 MAX. \"The market is a little bit slower but (our) target is still the same,\" said Airbus chief commercial officer John Leahy, who had downplayed the planemaker\'s chances of big orders at Farnborough ahead of the show. The biennial Farnborough gathering is a key event in the civilian and military aviation calendar and typically sees Airbus and Boeing battle it out for orders. This year\'s event has been a relatively subdued affair compared to other recent major airshows given the backdrop of a weak global economy and government cutbacks to military spending. Boeing\'s 737 MAX is an upgraded and more fuel-efficient version of the 737, the world\'s best-selling commercial airplane, with first delivery due in 2017. Airbus says the A320neo, due to enter service in late 2015, will use 15 percent less fuel than its current best performing A320 model. Boeing\'s deal with United Airlines will help the US manufacturer close the gap with Airbus in the battle for this segment of the market. Airbus has won more than 1,400 firm orders for its A320neo while Boeing had 549 firm orders for the MAX prior to the expected United announcement later on Thursday.