Occidental Petroleum was among the first major U.S. oil drillers to make a big bet on the resurgence of domestic production, spending billions to grab oil patches from Texas to North Dakota.
If costs start to slip, the explosive output growth could keep a lid on U.S. oil prices, regardless of tensions with Iran that have threatened global supply. If they continue to rise, breakneck output growth may stall as more companies follow Occidental's lead and begin to pare back drilling and investment.
The two biggest plays -- the Williston basin in North Dakota and Eagle Ford in Texas -- produced an estimated 1.2 million barrels per day (bpd) in April, close to the output from OPEC member Algeria, according to data from analytics company Bentek Energy. A year ago, they were producing only a third as much.
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