In an attempt to better understand the thermal history of the Ahnet and Reggane Basins, the techniques of apatite fission track analysis and zircon fission track analysis were employed on samples from a number of exploration wells previously drilled in the study area. The results indicated clear evidence for a major heating event at c. 200 Ma, overprinted on the effects of heating caused by simple burial before the Hercynian uplift. It is proposed that at least two major phases of hydrocarbon generation took place within the study area; an early, pre-Hercynian phase, in which chiefly liquid hydrocarbons were expelled and a later phase, associated with a 'heat spike' at c. 200 Ma, in which significant quantities of dry gas were generated and expelled