Boeing Co and the North American unit of Airbus parent EADS are competing for a U.S. Air Force refueling plane contract worth about $35 billion.
A decision is expected later on Thursday.
Following are highlights about the rival bids.
Boeing has said it will offer the Air Force an updated 767-based "NewGen" tanker with a digital flight deck from its 787 Dreamliner and a new fly-by-wire refueling boom.
It says the new twin-engined tanker would meet the Air Force's 372 mandatory requirements and burn 24 percent less fuel than the Airbus A330-based tanker that EADS will offer.
Boeing, keen to avoid the "Frankentanker" label opponents used to describe its offering in the last competition, has offered few details about the configuration of the new plane.
Industry sources say it will be considerably simpler than the last one, which included parts of different 767 models and was downgraded as possibly risky to produce by the Air Force.
Analysts say the 767, about 159 feet long with a wingspan of 156 feet, should be cheaper to build than the larger A330.
It is expected to have Pratt & Whitney engines.
In the last competition, Boeing's 767 tanker would have carried 190 passengers and 19 pallets of cargo.
The maximum fuel capacity would have been over 202,000 pounds, compared to around 250,000 pounds for the A330.
Boeing plans to build its 767 airplanes in Everett, Washington and modify them for military use in Wichita, Kansas.
An earlier design of 767 tanker was ordered by Italy and Japan. Japan has received all four of its Boeing tankers and they are in operational use.
The Italian tankers were delayed after running into problems with wing "flutter" and integration of the hose and drogue refueling pods.
Europe's EADS is offering a tanker plane based on the two-engined Airbus A330-200, which is larger than the 767.
EADS says the plane is a version of the "KC-45" platform with which it won a previous competition together with Northrop Grumman in 2008. That award was thrown out on appeal from Boeing and Northrop pulled out of the current rematch.
The KC-45 is EADS's name for the U.S. military version of the A330-based MRTT, or Multi Role Tanker Transport.
A total of 28 such tankers have been ordered by Australia, the UAE, Britain and Saudi Arabia. Delivery of the first Australian tanker has been delayed to later this year.
EADS says the plane's fly-by-wire refueling boom system has a fuel offload rate of 1,200 U.S. gallons per minute.
Part of the boom on a plane being developed for Australia was lost in mid-air during testing in January.
The Airbus plane has a wingspan of just under 198 feet and is almost 193 feet long.
It can carry over 250 troops or 32 pallets of cargo or evacuate 130 wounded plus intensive care and medical staff.
It would have engines from General Electric.
Like Boeing, EADS officials say the plane will meet all 372 requirements stipulated by the U.S. Air Force.
If EADS wins, the plane will be assembled in Alabama.
(Compiled by Andrea Shalal-Esa, Tim Hepher)