Domestic oil producers may have been too successful over the past few years, oilman Boone Pickens said Tuesday.

Speaking by phone on CNBC, Pickens said American oil has flooded the market much like domestic natural gas did a few years ago. The result of the shale oil boom is that the United States is the world’s only growing oil supply, and that growth has outpaced global demand.

If the price stays where it is or continues falling, domestic production will soon decline, Pickens said.

“We are feeling the pain right now,” he said. “When you feel the pain, you’ll cut your capex (capital expenditure) and the drilling will slow down.”