Mass spectrometry (MS) of the porphyrin fraction of a demetallated shale oil from the LLNL Hot-Recycled-Solids retorting process exhibited homologous series of C-25 to C-33 (C-28 maximum) for etio and C-26 to C-36 (C-30 maximum) for DPEP (isocyclic) porphyrins, respectively. The sum of intensities after baseline correction yielded a Sigma DPEP/Sigma etio ratio of 1/1. The petroporphyrin fraction was prepared by demetallation of the whole shale oil using methane sulfonic acid followed by isolation which involved extraction and purification by alumina chromatography. MS examination of silica purified fractions showed another type of homologous series, tentatively assigned as tetrahydrobenzo-DPEP por-phyrin. MS examination of porphyrin fractions isolated by alumina or alumina/silica chromatography without demetallation indicated Ni(etio) and Ni(DPEP) (isocyclic) porphyrins were observed with the same homologous series as seen in the demetallated fraction.