After a near sellout of their $9 one-way fares in two days, Hawai'i's three major interisland airlines said they have extended the offer.

Discount carrier go! fired the first volley in the latest round of the fare ware, announcing Sunday that it was lowering one-way interisland fares to $9 for travel between June 1 and Sept. 30. Competitors Aloha Airlines and Hawaiian Airlines matched the offer.

Yesterday, go! said it would extend the $9 offering for mid-week travel between May 29 and Dec. 15. The extension came after the airline sold virtually all of its $9 seats in the original offer. Again, Hawaiian and Aloha matched go!

None of the airlines say how many tickets they plan to sell at the $9 price.

Restrictions apply and tickets must be purchased by Friday from the airlines' Web sites. The $9 fare is good for Tuesday through Thursday travel and is subject to blackouts on days surrounding July 4, Thanksgiving and Labor Day.

A unit of Phoenix-based Mesa Air Group Inc., go! touched off a price war when it opened for business in Hawai'i on June 9, 2006 with fares as low as $19.

Aloha executives have said that all three interisland carriers are losing money when they sell interisland tickets below $50.

Hawaiian lost $11.9 million during the first quarter, while go!'s parent Mesa lost $24 million during the same period. Aloha, which is privately held, lost $8.5 million during the quarter ending Dec. 31, 2007.

Reach Rick Daysog at rdaysog@honoluluadvertiser.com.