470; TAI>4) and microscopically have no fluorescing liptinite macerals. In comparison, the Sarchahan Formation is evaluated as a good and effective hydrocarbon source rock (TOC>1%; Ro%=1.15-1.20; TAI=3+). The organic matter is chiefly composed of liptinite group of macerals including lamalginite and telalginite (type II kerogen) which are brown under white light and weakly fluoresces under UV excitation. In addition, the other maturity indicators such as clay minerals and crystallinity of illite are in agreement with organic petrography suggesting that Sarchahan Formationn  is  thermally  mature  and  is at catagenetic stage of hydrcarbon generation (end of oil generation window and the beginning of gas generation zone). The Seyahou and Sarchahan formations formerly referred as Gahkum Fm. by previous workers (1978) were reported to be overmature and have reached graphitic stage. The lower Silurian shales (Sarchahan Fm.) is correlated stratigraphically with Silurian hot shales from Saudi Arabia, where their petroleum source potential have already been approved. This paper supported by new experimental data elucidates and emphasis the importance of petroleum potential of Paleozoic strata for future hydrocarbon exploration in Iran.  ]]>