Oil prices will have to plunge at least another $20 per barrel “to choke off” the U.S. energy boom, according to The Wall Street Journal.

Smaller producers will face problems before that happens, and lower prices mean drilling companies won’t have as much cash to cover their loans. The downturn is expected to take a bigger toll in developing formations, like the Tuscaloosa Marine Shale, which belts Louisiana’s midsection.

However, energy firms haven’t put the brakes on production, and the number of drilling rigs has risen slightly since oil prices peaked.