Since being declared extinct in the wild in 1972, the Arabian oryx has been the subject of intense and sustained effort to maintain a healthy captive population and to reintroduce the species to its ancestral range. Previous reintroductions and associated genetic assessments focused on the release of closely managed zoo animals into Oman and included observations of inbreeding and outbreeding depression. Here we describe the use of multiple unmanaged herds as source populations for a new reintroduction project in the United Arab Emirates, allowing a comparison between studbook management and uncontrolled semi-captive breeding approaches to the conservation of genetic diversity. Results of mitochondrial control region sequencing and 13-locus microsatellite profiling highlight a severe lack of diversity within individual source populations, but a level of differentiation among populations that supports the formation of a mixed founder herd. The combined release group contained a similar level of diversity to each of the intensively managed captive populations. The research includes the first genetic data for animals held on Sir Bani Yas Island, a former private reserve which until recently held over 50% of the world's Arabian and scimitar-horned oryx and is recognized as having huge potential for re-establishing endangered antelope species in the wild. The genetic assessment provides the first stage of an ongoing genetic monitoring programme to support future supplemental releases, translocations and genetic management of reintroduced populations.