The molecular carbon isotopic composition of pyrolytically generated gaseous and non-gaseous compounds was monitored by compound specific isotopic ratio mass spectrometry. The instrument used for this study was a modified commercial GC-C-IRMS system onto which a micro-scale sealed vessel (MSSV) injection assembly has been mounted. The use of two different GC columns (Poraplot Q for gases and SE 54 for liquids) permitted analysis of the δ 13C of the pyrolysates for their C 1−C 30 + n-alkane content. In addition, CO 2 could be analysed together with the methane to hexane content in a single GC-C-IRMS run. Data obtained from the analysis of asphaltenes were contrasted with those obtained from the molecular isotopic analyses of their parent oils. Additional materials including sediments, coals, and humic matter were amenable to the MSSV pyrolysis procedure and provided isotopic information that could be exploited in terms of kerogen type but failed to show any maturity relationships. A relationship between the isotopic composition of pyrolytically generated carbon dioxide and the depositional paleoenvironments of candidate source rocks was found.