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This paper presents the results of a number of new studies in the Karama and Lariang onshore basins of western Sulawesi. The basins form part of an original west-facing, extensional half-graben system related to Eocene rifting centered on the Makassar Straits. Extension continued until the basins were inverted in the Plio-Pleistocene, during a contractional event. The majority of shortening was taken up by a suite of NW-SE oriented strike-slip faults which dissect the original extensional basin architecture. These strike-slip faults compartmentalize a series of contractional structures (folds and thrusts) that are related to a localized fold-thrust belt. Where the fold-thrust belt continues into the offshore, it is restricted in aerial extent by the Paternoster Platform in the south and the Palu Fault in the north. Palaeogene extension started in the Middle Eocene, resulting in deposition of a syn-rift sequence consisting of fluvio-deltaic sands, coals, lacustrine shales and limestones and laterally equivalent basinal marine facies. This sequence is overlain by a marine sequence of shales of Late Eocene to Early/Mid-Miocene age. Extension and contemporaneous intrusion and extrusion of igneous material continued through the Middle to Late Miocene and into the Early Pliocene during post-rift thermal subsidence related to subduction roll-back. Marine conditions persisted into Plio-Pleistocene times and sedimentation patterns became more complex with deposition of shelf muds, gravity flows and volcaniclastics being locally sourced from structural highs which form as contractional folds grow in the inverting basins. Rapid uplift across strike slip faults during this time also led to deposition of debris flows in what has previously been referred to as a foreland basin setting. The presence of an active petroleum system is demonstrated by the occurrence of oil and gas seeps over major fold structures (Karama and Lariang), and along the faulted, eastern margin of the coastal basin (Karama). These hydrocarbon seeps were generated from source rocks containing terrestrially-derived organic matter such as the Middle to Late Eocene, fluvio-deltaic coals and carbonaceous shale. Geochemical analyses of the oil seep samples indicate they are paraffinic, low sulfur, moderately low wax to waxy oils. The GCMS biomarker data of two oil seeps from the Lariang Basin were generated from an organic assemblage dominated by terrestrial higher plant material with some minor algal input. The oil seeps from the Karama Basin indicate derivation from a source rock facies containing algal debris mixed with some terrestrial higher plant material and are assigned to oil of an open marine/deep lacustrine source.