The Arabian oryx (Oryx leucoryx) historically ranged across the Arabian Peninsula and neighboring countries until its extirpation in 1972. In 1963–1964 a captive breeding program for this species was started at the Phoenix Zoo (PHX); it ultimately consisted of 11 animals that became known as the ‘World Herd’. In 1978–1979 a wild population was established at the Shaumari Wildlife Reserve (SWR), Jordan, with eight descendants from the World Herd and three individuals from Qatar. We described the mtDNA and nuclear genetic diversity and structure of PHX and SWR. We also determined the long-term demographic and genetic viability of these populations under different reciprocal translocation scenarios. PHX displayed a greater number of mtDNA haplotypes (n = 4) than SWR (n = 2). Additionally, PHX and SWR presented nuclear genetic diversities of N¯AN¯A = 2.88 vs. 2.75, H¯OH¯O = 0.469 vs. 0.387, and H¯EH¯E = 0.501 vs. 0.421, respectively. Although these populations showed no signs of inbreeding (F¯ISF¯IS ≈ 0), they were highly differentiated (G′′STGST′′ = 0.580; P