Commercial oil deposits in basement rocks are not geological 'accidents' but are oil accumulations which obey all the rules of oil sourcing, migration and entrapment; therefore in areas of not too deep basement, oil deposits within basement rocks should be explored with the same professional skill and zeal as accumulations in the overlying sediments. Landes et al. (1960), American Association of Petroleum Geologists Bulletin.
Petford, N., & McCaffrey, K. (2003). Hydrocarbons in crystalline rocks: An introduction. Geological Society Special Publication, 214, 1–5. https://doi.org/10.1144/GSL.SP.2003.214.01.01