Abstract: This work is carried on samples taken from wildcats drilled in Eastern Anatolia. The followinganalyses have been done on these samples : whole rock paragenesis, clay mineral paragenesis and its distribution,and calcite/dolomite ratio- From these results we tried to interpret the origin of petroleum.Illite is very rare or absent in all the investigated samples, so that we could not find the relationship between illite crystallinity index and burial diagenesis.The most abundant clay minerals are smectite, chlorite and kaolinites. The minor minerals are illite, disordered illite-smectite mixed layer clay minerals and corrensite.There are smectites in all the investigated samples of Pasinler-2 and 3 wildcat wells which are drilled in theErzurum-Pasinler basin. There results show that organic maturation is not reached in these levels.Similarly, there is smectite in all the investigated samples of Neftlik-1, 2, 3 and 4 wildcat wells which aredrilled in the Erzincan-Çayırh basin. These results also show that organic maturation is not reached in these levels.The clay mineralogical composition of samples of Tuzluca-1 wildcat well which is drilled in Kars-Tuzlucabasin shows that burial diagenesis is not completed in these levelsSamples taken from Hacilar-5, 6, and 7 wildcat wells which are drilled in the Malatya-Darende basin showthat there is a thrust fault in this area. This result is also confirmed by other geological investigations. There arepossible levels of reservoir rocks in all the investigated drillholes as indicated by calcite/dolomite ratios.