Thermo-simulation was mede on mudstone source rocks of the Wenchang Formation drilled in the Pearl River Mouth Basin. The result indicates that the abundant C

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4-methyl steranes contained in the source rocks were thermally stable. Nevertheless

the source rocks were the products of special dipositional environment

andwere part of the significant oil sources in the basin since they contributed abunhant C

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4-methyl steranes to the crude oils found in the basin. Therefore

it would be much helpful for oil-source correlation and reserve assessment of the basin if a thorough investigation on the source rocks is made. In addition

after 400℃ and 500℃ heating

another configuration of C

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4-methyl steranes was identified from the extracts

of which the origin may have two probabilities.