$972 Cheap United flights Porto (OPO) to San Diego (SAN)

Use the "Price (lowest to highest)" filter on Expedia to search for cheap United Airlines round-trip flights from $892 from OPO to SAN. Affordable one-way tickets from $972 are also on offer.**These prices were available on Expedia within the past 7 days, for flights departing within the next year. Prices and availability are subject to change. Additional terms apply.

To find cheap flights from OPO to SAN with United Airlines, start searching about one month before your intended departure. You can save 17% when you book your international tickets 18 to 29 days ahead instead of booking four to five months in advance. Another tip? Booking on Sunday can lead to average savings of 17% compared to Friday (the most expensive day).**Ideal booking window recommendation is based on average round-trip ticket prices for January through November for 2024. Best day of the week to book recommendation is based on average round-trip ticket prices for January through October 2024. All data sourced from ARC's global airline sales database.

Filter your results by "Morning" and "Early Morning" to find the earliest departures from OPO to SAN. Leaving early means flight cancellations are less likely.**Most reliable time of the day recommendation is based on January through August 2024 flight status data sourced from OAG's global flight data platform.

A rewarding loyalty program and the opportunity to collect points through United Mileage Plus are the start of the reasons to travel from OPO to SAN with United Airlines. Plus, by joining Expedia's free One Key™ program, you can earn OneKeyCash™* alongside United Airlines's loyalty program earnings. You can put it toward your future trips.*OneKeyCash™ disclaimer - OneKeyCash™ is not redeemable for cash and can only be used on Expedia, Hotels.com and Vrbo.