AirHint found the following cheapest return flights from St. Louis (STL) to Barcelona (BCN) in September 2025 (see full year).

Return flights

30 Sep - 07 Oct	United
24 Sep - 01 Oct	United
16 Sep - 23 Sep	United
10 Sep - 17 Sep	United
28 Sep - 05 Oct	United
08 Sep - 15 Sep	United
26 Sep - 03 Oct	United
14 Sep - 21 Sep	United
06 Sep - 13 Sep	United
19 Sep - 26 Sep	Frontier Airlines
20 Sep - 27 Sep	United
19 Sep - 27 Sep	Frontier Airlines
19 Sep - 24 Sep	Frontier Airlines
22 Sep - 29 Sep	United

Also check the deals for one-way flights from St. Louis to Barcelona 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 St. Louis to Barcelona in September from 490€

Return flights