The tax shield is a little-known advantage to Chevron’s mega-takeover of Hess struck last month. The tax benefits are expected to provide the No. 2 U.S. oil and gas producer hundreds of millions of dollars in extra annual cash flow over the next several years.

The 1918 Revenue Act first allowed corporations to carry their losses forward as tax benefits to smooth out large fluctuations in income over time. But the losses only come in handy if a company is eventually able to make enough money to have big tax bills.

Before the companies agreed to the $53 billion all-stock deal, Hess was sitting on more than $15 billion in net operating losses from previous years and unable to take advantage of them due to low profits and heavy losses, according to explanations Hess has provided in its financial statements.