Mass production of pyrolysis instrumentation such as the "Rock-Eval" has led to general application of whole-rock pyrolysis as a means of identifying and characterizing petroleum source beds. One of the problems inherent in the whole-rock technique is the effect of petroleum or bitumen on the measured amount of thermally extracted hydrocarbons from the kerogen.

Under pyrolysis, migrated oil or bitumen in the rock gives a major response near 250 to 350°C on the program (S1). However, solid bitumen and the "heavy-end" fraction of petroleum produce a measurable response (S2) in the 350 to 450°C range as well as in the same region where kerogen conversion to hydrocarbons occurs. Thus, large quantities of bitumen or migrated petroleum in rocks can affect the size and the maximum temperature of the S2 peak and can cause nonsource rocks to be misidentified as source rocks. These problems can be overcome by rinsing the sample in a chlorinated hydrocarbon solvent prior to analysis.