Sheffield is no stranger to volatility. He founded his Austin-based oil and gas company in 2008, and expanded it during the ensuing economic down years, leasing thousands of acres in the Midland Basin. It’s been a wild ride since, with a successful IPO in 2014 that made Sheffield a billionaire, followed by years of sinking oil prices. Today, the price of a barrel is floundering around the $50 mark. But Parsley Energy is ramping up production.