Alaska and Delta Airlines on Tuesday each announced plans to expand service at Sea-Tac Airport.

Delta’s Vice President for Seattle, Mike Medeiros, told the Port of Seattle Commission that “in the near future, our plans will be to nearly double the 86 departures that you see here this summer.”

Earlier, the airline issued a news release saying it planned to add service from Sea-Tac to Spokane, Maui,  Bozeman, Calgary, and Cabo San Lucas and Puerto Vallarta in Mexico in the months ahead.

Alaska issued its own release saying next spring it would increase daily departures from Sea-Tac from 253 to 280, an 11 percent jump. The airline plans to add additional flights to existing and previously announced new destinations.

Increased demand at Sea-Tac is leading the Port of Seattle to pursue terminal upgrades, including a new international arrivals facility. The airport is also pursuing a renovation of the north satellite, which serves Alaska Airlines.

The project, originally estimated to cost around $315 million, could grow to as much as $490 million, under a new estimate presented Tuesday. To meet demand, the airport is now considering adding nine new gates to the north satellite instead of four, bringing the total to 20.

Commissioner Bill Bryant called the need to renovate the 1970s-era terminal “a good challenge to have.”

“At least we’re talking about how to refurbish it for growth,” Bryant said. “There are a lot of airports around the country that are talking about which terminal to mothball.”

The airport says renovations are paid for with concession and parking revenue and by charging the airlines, who then pass on the cost to passengers. The airport estimates the cost of renovations will mean cents on the dollar for each ticket. At a presentation before the port commission, an Alaska Airlines executive suggested ticket prices could go up around 67 cents.

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