$99 Cheap American Airlines flights St. Louis (STL) to Harlingen (HRL)

Landing cheap one-way American Airlines flights from STL to HRL from $99 on Expedia is a cinch — just filter by "Price (lowest to highest)." Alternatively, check out our budget-friendly return fares from $199 for your next exciting adventure.**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.

Look for affordable American Airlines flights from Lambert-St. Louis Intl. Airport (STL) to Valley Intl. Airport (HRL) one to three months ahead of your day of departure. Travelers who book domestic flights 34 to 86 days in advance can save 25% compared to those who book just 6 to 12 days ahead. No matter the fare type and itinerary, the best day of the week to book a domestic flight is usually Sunday and the most expensive day tends to be Monday. Passengers who book on a Sunday can save 6% on average compared to those who book their travel on a Monday.**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.

Search American Airlines's earliest flights from STL to HRL by selecting the "Morning" and "Early Morning" filters. Not only will you arrive sooner, early departures are also 20% less likely to be canceled.**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.