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Two areas of shale diapirism in a deltaic setting were examined using 3D seismic data from offshore Brunei to determine the origin, evolution and geometry of shale diapirs. The study areas cover parts of the Egret and Ampa fields within the Baram Delta province. The Ampa diapir consists of a small bulge of the mobile Setap shale around which lies a zone of chaotically disrupted country-rock reflections. At the crest of this chaotic zone, vertical, cylindrical shale pipes arise that end in a wider head. The diapir heads wear halos of high amplitude reflections, probably due to the presence of methane gas. The Egret data show the same features, except that the bulge of the source layer is not detected due to low reflectivity and chaotic reflections at the base of the overburden. The bulging of the Setap shale on the Ampa data is interpreted as modified reactive diapirism in response to differential loading. The initial reactive …