Alligator gar (Atractosteus spatula) populations are declining in the southern United States and Mexico, prompting increasing efforts by state and federal agencies to manage populations. We sampled the alligator gar population in the Red River drainage of Oklahoma–Texas from March 2006 to April 2008 to evaluate population characteristics, identify efficient sampling techniques, and evaluate aging techniques. Catch rates for adult fish were highest using multifilament trammel nets (n = 80) during cold water periods (<12°C) and for young-of-year fish using mini-fyke nets (n = 60) during warm water periods (>18°C). Movements and home range were examined using ultrasonic telemetry. Home-range areas of six individuals were from 4.93 to 17.13 km² during a 4–9-month period. Spawning in Lake Texoma was documented in spring 2007. Sixty-four alligator gar were aged using double-blind methods of scale cross sections. A subsample of 14 individuals was also aged using whole otoliths to cross-reference scale ages. Age determinations ranged from 0 to 28 years at date of capture and suggest that the youngest gar were spawned in 2006 and 2007. Age determination of alligator gar using scale sections proved to be imprecise and biased toward overestimation of age in adults when compared with whole otolith ages. The alligator gar population in Lake Texoma and the Red River upstream of the reservoir appeared to be stable, represented by varied age and length classes, and is experiencing regular recruitment.