The Levantine Basin in the Eastern Mediterranean has become an attractive area for oil and gas exploration due to recent discoveries of major gas fields in the pre-salt sequences. Information on whether the gas in these new discoveries is of thermogenic or biogenic origin was restricted for a while, as the strategic implications are clear: if the gas is thermogenic, then deeper thermogenic oil potential could be lower or even excluded. However, if the gas is biogenic, an opportunity could exist for deeper thermogenic systems which could include oil. It is now known that the gas is predominantly of biogenic origin in Tamar, Leviathan and Aphrodite, with possible minor thermogenic contributions. As a result, exploration for deeper thermogenic systems and especially for oil is now planned in the Levantine. This shows the importance of understanding the processes which resulted in the formation of the newly discovered gas fields.