AirHint found the following cheapest return flights from Portland (PDX) to San Francisco (SFO) in September 2025 (see full year).

Return flights

30 Sep - 04 Oct	Spirit Airlines
26 Sep - 29 Sep	Frontier Airlines
27 Sep - 29 Sep	Frontier Airlines
25 Sep - 28 Sep	Frontier Airlines
28 Sep - 01 Oct	United	direct
30 Sep - 04 Oct	United	direct
26 Sep - 29 Sep	United	direct
27 Sep - 29 Sep	United	direct
25 Sep - 28 Sep	United	direct
25 Sep - 25 Sep	United	direct
19 Sep - 22 Sep	Frontier Airlines
17 Sep - 23 Sep	United	direct
19 Sep - 22 Sep	United	direct

Also check the deals for one-way flights from Portland to San Francisco in September.

The deals are updated regularly. The prices may go up as tickets are purchased by other travellers. Only the cheapest flights are offered. Select a price to book and secure these cheap prices.

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Cheapest return flights from Portland to San Francisco in September from 198€

Return flights