The effect of oil prices on the U.S. economy used to be straightforward: Higher was bad. Yet between 2014 and early 2016, as oil collapsed, growth slowed sharply. Since then oil has doubled, yet the economy has accelerated.

Credit this to the emergence of the U.S. as a leading oil producer and, soon, net energy exporter. More expensive oil is still a tax on consumers. But that tax is increasingly offset by the boost to energy investment, production and jobs. The U.S. business cycle is thus now tied in complex and surprising...