Before we can make any progress toward a sustainable energy future, we need to learn from our past and present. Although proven reserves of fossil fuels may continue to meet our energy needs for some years to come and nonconventional sources of fossil fuels are pushing back the “end” of oil, there will come an end, particularly because our reliance on fossil fuels remains great (recall Figure 1.2). The story of fossil fuels is a fascinating mix of history, politics, and science, with global security, economics, and most certainly the environment demanding that we begin to phase out our dependence on fossil fuels. The aim of this chapter is to understand what fossil fuels are, where they came from, how we got to this point, and where we are going with respect to nding fossil fuels for the foreseeable future. (N.B. Appendix IV provides some additional information with respect to units and conversions peculiar to the oil and gas industry.)

Contrary to popular belief, deceased and decomposed dinosaurs are not the primary source of fossil fuels that we use to power our planet. But before we can fully understand the source of petroleum (literally “rock oil”), we need to review a little geology. Scientists have devised many cycles to explain the processes and conversions of our planet, such as the carbon cycle to explain the chemical fate of carbon in the environment. The analogous rock cycle explains how rocks (far from sedentary objects) are moved about by internal and external processes on and in our planet. In this cycle, igneous, metamorphic, and sedimentary rocks are transformed and transported. We are most concerned with sedimentary rocks for they are the source of oil and gas. Produced from sediments deposited either on the land or at the bottom of a body of water, sedimentary rocks represent only about 5% of Earth’s crust (Skinner and Porter 2000). Sediment-and hence, sedimentary rocks-comes from everywhere and everything, including rock fragments, chemical precipitates (e.g., calcium carbonate from bones and shells), long-dead marine organisms, and detritus in general. In the sedimentation process, various kinds of materials are stratied such that sandy sediments (sandstone) overlay clay sediments (shales), with calcium carbonate-containing sediments (limestones) at the bottom of the strata. Sediment is buried and compacted to become sedimentary rock, typically at or near the site at which it was originally deposited. As a result, oil (which ultimately comes from sedimentary rock, vide infra) is not widely distributed on the planet, with obvious geopolitical consequences.