Now, shale drillers are the low-cost leaders

Technical advances in horizontal drilling have transformed shale oil into the most cost-effective and fastest sector in the US petroleum industry. Fracking operations in the American West are now considered the global swing producer, instead of Saudi Arabia.
As efficiency has risen and costs have fallen, shale now supplies 2/3 of the natural gas and 1/3 of all oil production in the US. The industry is now turning its attention to addressing environmental concerns over fracking.

The global oil glut began in 2014, as OPEC increased production to destroy its foreign competition. These actions was chiefly aimed at the huge oil boom in American shale oil operations, which had made the US nearly self-sufficient.
As oil prices fell under $100 a barrel, then under $70, then under $50, the easy loans that fracking companies used to fund operations dried up. Every drop in the price of crude reduced the value of the oil reserves they had on the books, and made it harder to roll over their debt.
Those oil companies that had over-expanded or had ignored efficiency measures began to go under. Debt rating agency Fitch recently reported that almost 1/3 of oil drillers that used junk bond financing have defaulted on a total of $29 billion in debt, and anticipates that to balloon to $40 billion by the end of the year. This follows $13.6 billion in defaults last year. Eric Rosenthal, Fitch’s senior director of U.S. leveraged finance, noted that the recent oil rally to $50 a barrel was not enough to save many of the oil operations that are on the ropes. “It’s a matter of when rather than whether they’ll default,” he said. Bloomberg reports that at least 130 oil drilling and drilling services companies have gone under since January 2015, leaving behind $44 billion in debt that will never be paid off.
Those drillers who are left standing have proven to be the ones who could cut costs and raise efficiency enough to survive the worst oil bust in 30 years.