Boeing emerged as the sole bidder in both rounds conducted by South Korea's Defense Acquisition Programme Administration, the country's arms procurements agency.
Seoul, which awarded a contract for 40 F-15Ks to Boeing in 2002, was keen for a contest in the 2.3 trillion won ($2.5 billion) K-X programme to dispel claims that it is biased towards US military hardware.
However, manufacturers such as the Eurofighter consortium and Dassault chose to stay away, with industry sources saying that they were wary of taking part in a competition that could be weighted against them.
A contract for the new batch of 20 fighters is to be signed around February 2008 and deliveries are likely to take place in the 2010-12 timeframe.
Industry sources say that South Korea could open a tender for another 20 fighters around 2010, although some speculate that Boeing could get a single-source contract as the service will be keen to have the same type of fighter.
South Korea is also keen to get access to the Lockheed Martin F-35 Joint Strike Fighter programme in the next decade. It is also contemplating the indigenous development of a stealth fighter through its KFX programme, and studying a proposal from Korea Aerospace Industries for the F/A-50 - a light combat version of the T-50 advanced jet trainer.