Figures 1 and 2 are based on data presented by Schollnberger and show the dominance of fossil fuels in the energy mix at the end of the 20th century.
Figure 1 shows historical energy consumption in units of Quads, a unit of energy that is often used in discussions of global energy because it is comparable in magnitude to global energy values. One Quad equals one quadrillion BTU or 10^15 BTU. In SI units, one Quad is approximately 10^18 J. The source of energy is presented in the legend in the same order as it appears in Figure 1.
Beginning at the bottom of Figure 1, we see that fire wood, coal, oil, natural gas, water and nuclear energy were the major contributors to energy in the latter half of the 20th century. The dominance of fossil fuels in the energy mix at the end of the 20th century is illustrated as a percent of total energy consumed in Figure 2. Each percentage distribution shown in Figure 2 applies to the associated point in time.