Chevron bought 15.38 million shares of Hess' common stock via the open market, even as the companies work to complete their embattled merger.

Chevron bought about 4.99% of Hess Corp's common shares this year, reflecting its confidence in completing the planned acquisition of Hess, the oil giant said in a regulatory filing on Monday.

Chevron is on the verge of buying oil company Hess. But as Chevron waits to swallow its rival, it is snacking on Hess shares—at a discount to the implied acquisition price. Chevron revealed the purchase of 4.