Carbon-type analysis methods for obtaining the composition of the viscous fractions of petroleum have been developed and justified primarily with detailed analytical data on such materials. Several methods were evaluated, using data for pure compounds of high molecular weight synthesized by API Research Project 42. This study confirms the basic validity of the carbon-type analysis correlations. Data for noncondensed multicyclic aromatics do not agree well with the correlations for petroleum fractions. This leads to the conclusion that the multinuclear aromatics in petroleum are mainly of the condensed variety, in agreement with the work of API Research Project 6 on such materials.More detailed analytical data on the viscous fractions of petroleum are needed.