World energy consumption by energy sources. We prepare the figure based upon the numbers listed in the data source. See Sueyoshi and Goto (2017). The figure indicates that fossil-fuel components (i.e., oil, natural gas and coal) are major energy resources in the world, all of which are used for not only modern business (transport and industry sectors) and household sector but also military purposes. The fluctuation of oil price may influence the market condition of modern business because oil is the most important primary energy resource.