Complex organic compounds that occur in crude oils and bitumens. The term biomarker is short for biological markers that are used as indicators of the source from which bitumen/petroleum was derived. Biomarkers are composed mainly of carbon and hydrogen. The most common biomarkers are the n-alkanes, isoprenoids, steranes, triterpanes, diterpanes, and naphthenoaromatics. Biomarker analysis is used to evaluate various geochemical characteristics of oils and rock extracts, including organic facies, thermal maturity level, depositional environment, geologic age, source lithology and oil to source rock correlations.