The Boeing Company (NYSE: BA) and Cathay Pacific Airways have signed an agreement for the purchase of two additional Boeing 777-300ER (Extended Range) aircraft, exercising existing purchase rights and bringing the airline’s total 777-300ER commitment to 18 aircraft over the past six months.

Boeing said that Cathay Pacific ordered 12 of its 777-300ERs in December 2005, as well as four additional aircraft from the International Lease Finance Company.

Cathay Pacific reportedly plans to take delivery of the two new 777-300ERs in 2008. The aircraft are valued at approximately USD500m at list prices, and will be powered by General Electric GE 90-115B engines.