In the past decade two large oil fields and several large gas fields have been discovered on the continental shelf of East Malaysia together with some smaller oil and gas fields. Geologically, the shelf contains most of the postgeosynclinal younger Tertiary sediments of the

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Northwest Borneo orogene. The shelf widens to more than 300 km toward the south in Sarawak and measures about 100 km in the north in Sabah. Structural deformation is most severe onshore and decreases toward the offshore, where all the currently producing East Malaysian fields are located.

The two largest offshore oil fields, the Baronia field in northern Sarawak and the Samarang field in southern Sabah, are both situated in areas characterized by synsedimentary tectonics. Production is from upper Miocene coastal-plain and coastal sands, which have been charged with hydrocarbons from land-plant-derived source rocks.

The large gas fields are located offshore central Sarawak, and the gas is trapped in upper Miocene carbonate reefs.

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