Abstract: Since the founding of P.R.China, three geologic surveys and prospecting researches on petroleum Resources in marine sedimentary provinces of South China have been made, but the results are unsatisfied. The long-term overlooking of the organic matter metamorphism as one of important factors in hydrocarbon reservoir preservation condition and not taking it into consideration in the petroliferous prospect assessment system would be the major reasons. The study by means of the coal quality and fixed-carbon ratio shows that in Sichuan-Guizhou-Guangxi areas, gas fields could be possibly found in the lean coal or slight coaly metamorphism provinces with fixed-carbon ratio of less than 90%, in which the petroleum preservation conditions of Paleozoic were lost.

Key words: China, South China, marine deposit, organic matter metamorphism, fixed-carbon ratio, paleo-reservoir