In this study, H-1 NMR and quantitative C-13 NMR spectroscopies were used to investigate the chemical transformations of oil during the retorting process. Oil samples were obtained by the pyrolysis of Indonesian oil sands at various heating rates and final retorting temperatures. A modified Brown-Ladner method was used to determine the structural parameters of the samples. The results showed that the effects of the final retorting temperature on the chemical structures were significant, because decomposition and polymerization occurred during the retorting process. The chemical structure was also significantly affected by the heating rate, which influenced the degrees of distillation and pyrolysis. For comparison and accuracy, the equations proposed by Poveda and Molina (J Pet. Sci. Eng. 2012, 84-85, 1-7) were also used to calculate the structural parameters, based on a combination of the H-1 and C-13 NMR spectra. The observed trends in the changes in the structural parameters were similar for the two methods.