The burial of immature sediments beneath a thrust sheet may result in sufficient heating to generate hydrocarbons. We present a model for the thermally activated generation of oil from kerogen and the subsequent destruction of the oil through cracking. Using oil generation may begin soon after emplacement of the thrust sheet. Beneath thick thrust sheets (>8 km), all oil in the sedimentary section may be destroyed less than 5 m.y. after thrusting. In the sedimentary section beneath the Absaroka thrust plate in the Fossil Syncline of western Wyoming, Paleozoic and a part of the Mesozoic section were thermally mature prior to emplacement of the Absaroka Plate. The remaining part of Mesozoic sediments matured only after thrusting.--Modified journal abstract.