Kerogen maturation, estimated from pyrolysis Tmax values is compared with the smectite laayer‐content of the illite/smcetite mineral derived from sediments in six suites from different basins with different ranges of statographic age. The most significant correlations are made when camparing Tmax and estimated percentage kerogen transformation with sample age for the same smecite layer‐content (iso‐smectite content or stage of clay maturation) the percentate transformation of Type III kerogen and smectite layer‐content shows a regulare relationship at the end of the clay reaction series (10 smectite content), which includes the oil and gas potential range for sediments in the 200‐100 MM year age groups. Relations between less mature, more smectic illite/smectite clay minerals and kerogen maturation are not at pre