AirHint found the following cheapest return flights from Houston (IAH) to Porto (OPO) in September 2025 (see full year).

Return flights

22 Sep - 29 Sep	Air Canada
23 Sep - 30 Sep	Air Canada
04 Sep - 11 Sep	Spirit Airlines
12 Sep - 19 Sep	Spirit Airlines
03 Sep - 10 Sep	Spirit Airlines
13 Sep - 20 Sep	Spirit Airlines
24 Sep - 01 Oct	Spirit Airlines
20 Sep - 27 Sep	Spirit Airlines
18 Sep - 25 Sep	Spirit Airlines
06 Sep - 13 Sep	Spirit Airlines
05 Sep - 12 Sep	Spirit Airlines

Also check the deals for one-way flights from Houston to Porto 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 Houston to Porto in September from $608

Return flights