Subsurface sedimentary samples from various wells situated in the Jaisalmer basin (India) have been studied using Mossbauer spectroscopy. A possible correlation between the presence and the absence of Fe2+ in clay minerals in sediments and the quality of source rock is discussed. It is suggested that the distribution of Fe2+ in source rock sedimentary sequence could be a useful parameter when coupled with the other geochemical parameters in hydrocarbon prospecting.