The maximum palaeotemperature of oil-bearing sandstones in the UpperTriassic in the eastern Ordos basin has been determined by using many methods including thevitrinite reflectance, fluid inclusion, apatite fission track, illite crystallinity, chlorite polytypeand diagenetic change of authigenic minerals. The thermal gradient in the Late Mesozoic wasabout 2.9-3.0℃/100m. The Upper Triassic was in a mature stage of organic matter andhydrocarbon began to be generated and migrated during this period. The palaeotemperatures ofoil-bearing sandstones were in the range of 88-110℃; those for the generation and migrationof oil ranged from 112 to 122℃. The thickness of the denuded strata overlying the UpperTriassic was 2465-2750m. The present burial depth of oil-bearing sandstones is generally from400 to 1200m. At a depth of ca. 1900m, the temperature may reach 140℃. Below this depth,organic matter was supermature and mainly generated gas.