The central part of offshore Sarawak comprises a smooth continental shelf approximately 300 km wide that forms the easternmost part of the northern Sunda shelf. Geologically, it includes a large part of the younger Tertiary Northwest Borneo sedimentary basin, exposed in the Miri zone of Sarawak. Coastal-plain to deeper marine sediments of Oligocene to Holocene age form the basin fill and are developed in a series of eight regressive depositional cycles. Deformation of the area is most severe in the nearshore part or Balingian Province, where a wide belt of anticlinal structures is developed. The outer shelf area, or Luconia Province, is characterized by an extensive complex of Miocene reefal carbonate rocks formed during a period of maximum transgression.

Exploration of this shelf area has been carried out during the last 15 years by Sarawak Shell Berhad, since 1976 under the terms of a production-sharing agreement with Petronas. To date, many encouraging indications of hydrocarbons, including one oil field and several gas discoveries, have been found. Objectives include sands of coastal-plain and coastal origin in Balingian and reefoid carbonate rocks in Luconia.