Oil is king, but coal, natural gas gaining.

• Position: Energy Sources

Although oil remains the world's leading energy source, coal and natural gas continue to grow in significance, according to research conducted by the Worldwatch Institute, Washington, D.C.

Global consumption of coal increased 5.4% in 2012, to 3,720,000,000 tons of oil equivalent, while natural gas use grew 2.2%, to 2,910,000,000 tons of oil equivalent. Both are primary fuels for the world's electricity market and, because they often are used as substitutes for one another, their trends need to be examined together, write report authors Matt Lucky and Reese Rogers.

The bulk of coal use is for power generation, with smaller amounts being used in steelmaking. Spurred mainly by rising demand in China and India, coal's share in the global primary energy mix reached 28%--its highest point since the International Energy Agency began keeping statistics in 1971. Although the U.S. remains one of the world's largest coal users, just over 70% of global demand was in countries outside of the Organisation for Economic Cooperation and Development, including China and India. Consumption in non-OECD countries grew eight percent to 2,630,000,000 tons of oil equivalent.

China alone accounted for nearly half of all coal use. India is the second-largest contributor to rising coal demand and is the world's third-largest coal consumer, after surpassing the European Union in 2009. The U.S. remains the second-largest coal user, even though U.S. demand has decreased by around five percent due to the shale gas boom and the abundance of cheap natural gas. Even with declining demand, the U.S. accounts for 45% of coal demand within the OECD.

Coal production, like consumption, is concentrated mainly in China, but the U.S. holds the largest proved coal reserves, with 28% of the global total, followed by Russia (18%), China (13[degrees]/o), Australia (nine percent), and India (seven percent). Together...