Global benchmark Brent crude rose as high as $81.48 a barrel, its strongest level since Nov. 21, 2014. The contract ended Monday's session up $2.50 a barrel, or 3.2 percent, at $81.20, its best closing prices since Nov. 11, 2014, when it settled at $81.67.
Meanwhile, U.S. West Texas Intermediate crude rose $1.30, or 1.8 percent, to $72.08, its best settle since July 10.
Brent first hit a new four-year high in early morning trade. Oil prices extended gains at midday, and the contract's settle above $80 a barrel positions Brent for a breakout, said John Kilduff, founding partner at energy hedge fund Again Capital.
"From there then you could see a greater push higher, really to $83 or $85," he said. "That should engender follow-through buying."
J.P. Morgan wrote in its latest market outlook that "a spike to $90 per barrel is likely" in the coming months thanks to U.S. sanctions on Iranian oil exports, which have fallen dramatically in recent months as importers brace for the impending penalties. The bank forecasts Brent and U.S. benchmark WTI prices to average $85 and $76 per barrel, respectively, in the next six months.
A meeting of OPEC and non-OPEC oil ministers in Algiers over the weekend concluded with the 15-nation cartel and its allies refraining from an urgent boost in output, despite President Donald Trump's demands that it work harder to bring down prices. The ministers said they would increase output only in the event that customers wanted more cargoes.