There are a number of car rental options situated at the airport:
Chic Car Rent is a homegrown Thai company and has a number of car rental locations across Thailand including at Ubon Ratchathani Airport. The counter is situated just outside the terminal building.
Budget is a well-known international car rental company and has a counter at the airport.
Avis is an American car rental company with locations across Thailand.
The German company Sixt are represented at Ubon Ratchathani Airport.
Thrifty have a counter outside the terminal building.
Hertz are represented at the airport and have a wide variety of vehicles available for hire.