AirHint found the following cheapest return flights from St. Louis (STL) to Denver (DEN) in May 2026 (see full year).
Return flights
| 15 May - 20 May | United | direct | |
| 15 May - 19 May | United | direct | |
| 08 May - 10 May | Frontier Airlines | direct | |
| 07 May - 10 May | United | direct | |
| 22 May - 26 May | Southwest Airlines |
Also check the deals for one-way flights from St. Louis to Denver in May.
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