Hawai'i's airline industry is ushering in the new year with a new round of fare cuts.

Interisland carrier go! said yesterday that it was lowering one-way interisland fares for travel on Dec. 31 to $20.06. The state's two largest carriers, Aloha Airlines and Hawaiian Airlines, immediately matched.

On Tuesday, Island Air, the state's No. 3 airline, began offering $12 return tickets for round-trip flights through March 15. The $12 return ticket must be purchased by today.

The lower fares come as the interisland flights are already crowded due to holiday season discounting, travel agents said.

"There aren't a lot of seats available right now," said Rachel Shimamoto, manager of Travel Ways Inc.

All three airlines would not say how many tickets they will sell at the $20.06 price.

Aloha, Hawaiian and go! said the $20.06 tickets must be purchased by Saturday.

go!, a unit of Phoenix-based Mesa Air Group, triggered a fare war when it opened for business on June 9 with an introductory $39 one-way fare.

Since then, go! has lowered one-way fares to $29 on several occasions and to as low as $19. Aloha and Hawaiian have matched go! each time it has announced a discount.

The lower interisland fares come as several Mainland and international carriers have announced their own discounted fares.

United Airlines said one-way fares on its Chicago to Kona flights will cost $266 for travel through through March 7. Tickets must be bought by Jan. 7, United said.

Jetstar, the new low-fare airline operated by the Qantas Group, is offering a $289 one-way fare between Honolulu and Sydney or Melbourne in Australia to commemorate the launch of its new Honolulu service.

Reach Rick Daysog at rdaysog@honoluluadvertiser.com.