The Cenozoic sedimentary history of North Sumatra is reviewed and a new account of basin development is proposed that accommodates contrasting stratigraphic histories across the region, especially times of sudden facies change. Micropalaeontology and geohistory techniques have been used to estimate the magnitude of stratigraphic change and, together with the timing of events, this indicates that North Sumatra developed in a dynamic transtensional tectonic setting, as has been proposed in regional structural models, and not the back-arc setting usually assumed by oil industry workers. This style of basin development has direct control on the nature and areal distribution of the petroleum systems elements. New definitions of common formation terms are suggested, based on a well-constrained sequence stratigraphic model, which has been assigned a new nomenclature of NS10 to NS50 Megasequences. It is noted that the stratigraphic and geographic position and extent of the source rock for the Arun, NSO A, NSO J and South Lho Sukon giant gas and condensate fields is still not known. © 2019