San Diego International is quietly becoming one of the most competitive airports in the US. Southwest and Alaska Airlines have announced 17 new nonstop routes for 2026 and 2027, many already flying, in what looks like a direct game of one-upmanship between the two carriers.

The numbers are striking. Southwest will sell a record 13.3 million round-trip seats at SAN in 2026, up 20% year over year, giving it a 37% share of the airport's total capacity — its highest ever. Alaska, meanwhile, is up a remarkable 35% on its previous high, with 8.4 million seats. Together the two airlines have added 4.4 million extra seats to and from San Diego in a single year.

Alaska's six new routes include some genuinely useful additions: Tulsa from March 2026, Santa Barbara, Dallas/Fort Worth, Oakland (four daily E175s, a far stronger offering than the departed Spirit), Raleigh/Durham, and — the most interesting for holidaymakers — Loreto in Baja California Sur. That little Mexican resort town last had nonstop service from San Diego in 2006, so this is a genuinely new market, albeit a modest one: two weekly winter flights on a 76-seat Embraer E175 from December 19, 2026.

Southwest's 11 additions lean heavily on leisure destinations. Maui's Kahului, Puerto Vallarta, Seattle, Bozeman and Spokane all launched in early March 2026, reviving routes the airline flew before. New for Southwest are Santa Rosa in California's wine country, Boston from June, Santa Barbara from August, and two weekly flights to Kona and Lihue in Hawaii starting March 2027. Every one of these routes puts Southwest head to head with Alaska, and the pair now compete on 29 routes out of San Diego.

For travellers, this is mostly good news: more nonstops, more competition and, typically, better fares on overlap routes. California coverage is a highlight — Southwest now links San Diego to seven in-state airports including Fresno, Sacramento, San José and Santa Rosa, handy for road-trip-free weekenders. Watch the timing if you're booking, though: some routes are seasonal (Loreto is winter only, the Hawaii flights twice weekly), and with this much capacity flooding in quickly, some of these routes may not all survive the shakeout. If a route appeals, book it while both airlines are fighting for the same seats.