The study of natural products in plants, animals, bacteria, fungi, and other living systems has long been of interest to chemists, biochemists, and analytical chemists. Generally, however, these scientists are concerned only with the isolation and identification of compounds present in living systems. A relatively small but rapidly growing scientific discipline has emerged over the past two decades involving scientists primarily interested in the fate of organic material and associated natural products after their demise and deposition in the sedimentary record and conversion into fossil fuels or chemical fossils. Organic compounds present in the original source material whose carbon skeleton is preserved throughout the geological record are referred to as biomarkers. In this Report the authors will introduce some of the basic concepts of petroleum geochemistry and the key role that analytical chemistry has played in the development of this discipline. They will also discuss areas in which geochemical research is most likely to develop in the next few years, and they will examine the major analytical challenges the organic geochemist will meet in conducting geochemical research during the next decade.