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The Kutai sedimentary basin, situated along the eastern continental margin of Kalimantan, is one of the oldest and more prolific oil producing areas in Indonesia. The drilling for hydrocarbon began in the late nineteenth century and from 1969 to date, more than 90 exploratory wells have been drilled. The early stratigraphic subdivisions of the basin were based primarily on biostratigraphic zones using larger foraminifera. Presently, biostratigraphic zonation is being refined by using smaller planktonic and benthonic foraminifera, and calcareous nanoplankton. Sedimentation during the Early Tertiary was predominantly controlled by northern and southern source areas. Tectonic uplift of the Kuchmg High during Late Oligocene time resulted in a major shift of the sediment source area to the west. A high sediment infiux formed extensive constructive delta systems in Middle Miocene to Pliocene time, prograding from west to east. Hydrocarbon accumulations in the Kutai basin are found in progressively younger sedimentary rocks to the east and are within sandstone deposited in a delta front and delta margin depositional environment.