Sediment samples from various depths of wells GT-2, BT-1, MT-1 and KT-2 situated in Jaisalmer basin (India) have been studied. The iron is found mainly in the form of pyrite, siderite and clays. Small quantities of ankerite were also found in a few samples. The fluctuation in the amount of pyrite and siderite with depth indicates the fluctuation in redox conditions in these sediments. Possible correlation between redox environment and formation of hydrocarbons is discussed.