China Southern Airlines Corp. (ZNH) is seeking to sell four of its widebody Boeing (BA) 777-200 medium-range aircraft and has invited interested parties to submit bids, according to a tender invitation posted on the carrier's Web site this week.

The Guangzhou-based airline currently operates a fleet of 10 Boeing 777 aircraft, including six extended range models serving long-haul routes.

The four 777s it plans to phase out are the original short-range versions, which joined China Southern's fleet between 1995 and 2000.

The list prices of these aircraft were around US$115 million to US$143 million in the mid-1990s when purchased new, according to earlier reports.

China Southern, which was China's first airline to operate the 777s, didn't say why it wants to retire the planes given their relative young age. Passenger aircraft can remain in service for over 20 years, industry analysts say.

China Southern said in April it decided to lease eight Airbus aircraft it had on order instead of buying them, to help the company reduce its "tremendous" need for capital and relieve the pressure on operations caused by a high asset- liability ratio.

China Southern is China's biggest airline by fleet size. At the end of 2007, the carrier had a fleet of 332 aircraft.