Seven unweathered heavy residual oils, analyzed and compared for source identification purposes, demonstrate that the comparison of heavy residual oils must be performed with great care using a variety of analytical techniques and comparison methods. Furthermore, these methods are best applied to known common‐source pairs and to known non‐common‐source pairs in addition to the unknown pairs. Physical and chemical tests showed that, for the most part, these properties for the seven oils were within the error range of the test. Visual comparison of the chromatograms also showed that they were very similar. Normalized normal paraffin and isoprenoid peak height profiles, when subjected to measurement‐error and statistical comparisons, provided quantitative evaluations of the relative likelihood that the members of the various oil pairs were from a common source.