Abstract At the time being there are known some tens oil and gas fields in magmatic (Libya, United States, Venezuela, Russia, China, Egypt, India, etc.). The oil field Bachho (White Tiger) is confined to a horst-shaped granitoid massif - the basement - with a complex inner structure. The massif is located in the Central High of the Cuulong Basin on the shelf of South Vietnam. At the field there more than one hundred wells have been drilled, most of them are highly productive with oil flow rate up to 1350 t/d. The uniqueness of this field is the fact that the reservoir rocks are "fresh" granitoids not clearly touched by weathering processes; the oil column exceeds the amplitude of the structure; and the presence of hydrocarbon gases in the rock voids indicates to existence of some additional hydrocarbon sources 1. The rock composition of the basement is represented by differently dated granites, adarnellites, granodiorites, diorites, leucomonzodiorites, monzonites. The transition between the rocks is not always clear enough. Besides, the massif is dissected by numerous dikes of comagmatites of the Oligocene effusive rocks composed of diabases, basalts, trachibasaltic porphyrites which fonned a lava sheet over the basement and in the Oligocene terrigenuos sequence. Tectonic processes, pneumatogenic mineralization, hydrothermal activities Jed to rock alteration. As a result, there is not only increase of secondary porosity, but also enrichment of granitoids with secondary minerals (kaolinite, zeolite, calcite, chlorite, pyrite etc.) filling in secondary voids or developing over the feldspars. The increasing number of oil and gas reservoirs discovered in granitoid rocks as well as the regional oil-bearing of granitoids on the self of South Vietnam (the oil fields Dragon, Big Bear, Tamdao, Cuulong etc.) allows to admit a Society of Petroleum Engineers new type of reservoir rock - granitoid rocks - along those of terrigenous and carbonate rocks.