Based on observation of the clay-catalyzed conversion of the fermentation products of glucose to hydrocarbons and the related evidence from the literature, glucose is recognized as the primary precursor of petroleum. A multiple pathway of petroleum formation is presented. In aerobic growth of living cells, fatty acids and related products are generated from glucose which are buried and incorporated into kerogen during diagenesis, and finally converted to petroleum through catagenesis. By anaerobic fermentation, glucose may be converted into simple oxygenates which can be transformed into components of petroleum upon catalysis by clay. In-depth analysis of the chemistry involved suggested that a sequence of four basic chemical reactions, oxygen shift, decarboxylation, dehydration, and polymerization, is sufficient to effect the transition from glucose to hydrocarbons. Synthesis of petroleum hydrocarbons by existing industrial processes, namely fermentation and catalysis, appears to be feasible. Petroleum can therefore be considered as a renewable resource.