Asian airlines have also expressed interest in buying Virgin America, although they would have to partner with a U.S. bidder under foreign ownership rules governing U.S. airlines. JetBlue, Alaska Air and Burlingame, California-based Virgin America declined to comment. In the past year, Virgin America has faced steep declines in unit revenue, or sales relative to flight capacity, as bigger rivals have added seats to gain share and take advantage of lower fuel costs that make it cheaper to operate flights.