Self Service Avgas (100LL) is available 24/7, at two pumps at the Airport Terminal. Check KGTU fuel prices at airnav.com/fuel/local.html.
Full-service Avgas (100LL) is available through the FBO.
Full-service Jet Fuel (Jet-A) is available through the FBO:
Cutter Aviation: (512) 869-0900, firstname.lastname@example.org
600 S Hangar Dr, Georgetown, TX 78628
The Airport does not have self-serve Jet A fuel.