The organic matters of Rudeis and Kareem formation from Ras Budran oilfield in the central Gulf of Suez, Egypt, were investigated throughout the study of biomarkers and infrared spectrometric analyses. The results showed that Pr/Ph, Pr/n-C-17, and Ph/n-C-18 ratios indicated marine source organic matters deposited under reduced condition with a less effect of biodegradation and mature stage of occurrence. The gammacerane index indicated a low-salinity environment of deposition for the initial organic matters existed in the analyzed samples. Steranes distributions show high percentage of C-28 steranes and C-29 steranes compared with C-27 steranes, and low-concentration C-27 diasteranes show generally low ratios indicating anoxic carbonate source rocks. The diasteranes/steranes showed generally low ratios indicating most marine carbonate sources. The tricyclic terpane reflects mature organic matters and originated from marine organic sources.