Extracting shale oil at current prices can yield a modest return, Exxon Mobil Chairman and CEO Rex Tillerson told CNBC.
"[But] we wouldn't do that because we think our resources are worth more than that," Tillerson told "Squawk Box" in an interview that aired Thursday, a day after Exxon held its annual analyst day at the New York Stock Exchange.
"Our development costs in the Permian are about $10 a barrel now; the Bakken is down to $11. Our cash cost is $10," he estimated.
Located in Texas and New Mexico, the Permian Basin, the nation's most prolific oil-producing geological formation, has seen revival in recent years with the advent of horizontal hydraulic fracturing, or fracking. The Bakken Shale region, which has also seen a fracking boom, includes parts of North Dakota and Montana.
"When you get to $40 [per barrel], particularly companies that this is really all they have — it's a one-play opportunity for them — I expect there will be some volumes [coming back]," Tillerson said.