The Wall Street Journal reported North American oil-and-gas companies have more than $200 billion of debt maturing over the next four years, starting with more than $40 billion in 2020, according to Moody’s.

The Journal added easy credit and enthusiastic investors fueled the North American shale-drilling boom that flooded the world with oil and gas.

OPEC has curtailed its production to bolster prices, but U.S. companies kept drilling according to the Journal.