Drilling for oil in the Bakken shale formation in July 2013. Photo by Andrew Burton/Getty Images.

If $100 a barrel wasn’t enough to make a shale driller money, imagine what a price 40 percent lower is doing. Not good.

According to a Bloomberg Business report, debt is becoming a dangerous burden for an increasing number of players in the U.S. shale boom.

“The question is, how long do they have that they can get away with this.” The companies with the lowest credit ratings “are in survival mode.” – Thomas Watters, an oil and gas credit analyst at Standard & Poor’s in New York, according to Bloomberg.

Bloomberg said that “interest payments are eating up more than 10 percent of revenue for 27 of the 62 drillers in the Bloomberg Intelligence North America Independent Exploration and Production Index, up from a dozen a year ago.,” and added that drillers’ debt “ballooned to $235 billion at the end of the first quarter, a 16 percent increase in the past year, even as revenue shrank.”