Early this year, Scott Sheffield realized he had a problem. Investors were cooling on Pioneer Natural Resources Co., the company he built into one of the leaders of the American fracking boom.

Like many shale companies, Pioneer was pumping a lot but making little. It was spending hundreds of millions more than budgeted as it strained to meet a goal Mr. Sheffield set years back—producing a million barrels of oil and gas a day within a decade, enough to rival OPEC nations such as Libya.

So...