The number of U.S. oil drilling rigs fell by 158 from early December to mid-March… The return of oil prices to about $50 a barrel presents a test for an idea that gained currency early after the market’s long swoon began two years ago: the “shale band.” The term was coined back in May of 2015 by Olivier Jakob, managing director of Petromatrix, a consultancy based in Switzerland. Mr. Jakob said U.S. oil production trends would be determined by two price points —$45 a barrel, below which oil produced from shale formations would drop off, and $65 a barrel, above which there would be “massive [shale] production coming online.” In between was the shale band, a range where shale supply would be basically steady, according to Mr. Jakob’s theory. But it hasn’t quite worked out that way, with shale producers keeping the taps on at lower prices than many […]