The Taranaki Basin, situated on the west coast of the North Island of New Zealand, contains the only commercial gas and condensate fields found in New Zealand to date, Kapuni and Maui. These were discovered in 1959 and 1969 respectively.

The Upper Cretaceous and Tertiary infill of the Taranaki Basin represents a depositional mega-cycle affected by two tectonic phases: initial rifting and foundering during the Late Cretaceous and Early Tertiary, followed by wrench faulting, graben formation, and basin inversion during the Miocene and Pliocene. The Taranaki Basin consists of a Western Platform and an eastern Graben Complex. The former was relatively stable throughout most of the Tertiary and was affected by normal block faulting only in Late Cretaceous to early Eocene times. The latter comprises a tectonically complex graben system, which was particularly active during the Miocene. This Taranaki Graben Complex closes to the south and is bounded to the east by the major Taranaki fault zone, whereas to the west, the Grabe Complex generally shallows across a series of steep, normal and reverse en echelon arranged faults.

Late Cretaceous half-grabens accumulated thick sediment wedges ranging from coarse clastics to fine-grained coal measures. A marine incursion during the Paleocene was interrupted by an Eocene regressive phase, during which coal measures were deposited in southern and eastern parts of the basin. Quartzose sandstones in these coal measures form the reservoirs in the Kapuni and Maui fields. Regional subsidence resumed during the Late Eocene and Oligocene and resulted in the deposition of mainly marls and pelagic carbonates in the west and neritic limestones, sandstones, and/or mudstones in the east and south. During the Miocene development of the Taranaki Graben Complex, thick flysch-type deposits within the graben spilled over onto the Western Platform. From then on, through deposition f a thick sequence of "giant foresets," the continental shelf prograded across the Western Platform to its present limit.

Upper Cretaceous and Lower Tertiary coal measures form the main objectives in the Taranaki Basin; they provide source, reservoir, and cap rocks. The "Lopatin" method calibrated against measured vitrinite reflectance values was used for calculating source-rock maturation to outline potential hydrocarbon kitchen areas and to estimate the degree of maturity. The Taranaki Graben Complex is interpreted as a fully mature gas province, whereas the Western Platform shows decreased maturity to the west and northwest. Source rocks are confined to the coals and intervening carbonaceous shales. The coals are mainly hydrogen-poor, but intercalated lacustrine shales with resin and bitumen-rich layers may provide a more kerogenous source rock. Determination of the effective burial time of these sour e rocks is important in understanding the generation of hydrocarbons in the Taranaki Basin.