Crude oil markets are likely to balance some time next year as supplies from North America, including U.S. shale, continue to decline significantly, the chairman of Saudi Arabia’s giant oil company said Monday.

“Supply has plateaued in North America and [is] declining by significant amounts. We expect that to continue and perhaps accelerate in 2016,” Khalid al-Falih, chairman of Saudi Arabian Oil Co., known as Saudi Aramco, said in a news conference in Riyadh.

“We...