[en] The delta¹³C values obtained from 25 crude oil samples representing the main producing oil fields in Egypt indicate a significant difference between the Gulf of Suez Province and the Western Desert Province, which is attributed to environmental differences in the source rocks of the two provinces. Variations within each of the two provinces were compared and related to age, thermal maturity as well as migration processes. Variations of the delta¹³C values were also related to changes in the GOR (gas/oil ratio) and API gravity values