Thanks to the fracking revolution, in 2013 the United States surged past both Saudi Arabia and Russia to regain its spot as the world's top energy producer. Above, water pools near an oil pump outside of Williston, North Dakota. (See related story, "U.S. Edges Saudi Arabia, Russia in Oil and Gas.")

Analysts believe U.S. production topped 12.1 million barrels per day, surpassing the Saudis by some 300,000 barrels per day. In western North Dakota's Bakken shale, and in Texas' Eagle Ford and Permian basins, drillers applying the combination of hydraulic fracturing and horizontal drilling have been able to reverse what once was thought to be an inexorable decline in U.S. oil production. (See related, "The New Oil Landscape," and "North Dakota's Salty Fracked Wells Drink More Water to Keep Oil Flowing.")

Just in time for the 40th anniversary of the Arab oil embargo, which awakened the global drive for energy security, the United States finally might approach its goal of independence from foreign oil. (Take related Quiz: What You Don't Know About Oil Crisis History.) U.S. reliance on oil imports, which peaked at 60 percent of supply in 2005, is expected to fall to 25 percent by 2016. (See related, "IEA World Outlook: Six Key Trends Shaping the Energy Future.")—Marianne LavelleVote and Comment: "How Has Fracking Changed Our Future?"