(Bloomberg) -- Energy stocks rallied Monday to achieve their best day in six months as OPEC+’s surprise production cut boosted the price of oil.

The S&P 500’s Energy Index climbed 4.9%, the most since October 2022. The rally added roughly $79 billion in market value to S&P 500 Energy Index members, with Exxon Mobil Corp. accounting for about $26 billion of that tally. The oil giant is nearing the $500 billion mark for the first time since 2008. 

OPEC+’s decision to slash oil production lifted commodity prices, boosting energy stocks which had been languishing in 2023 after two years of outperformance. The sector has slumped nearly 1% this year while the broader benchmark has gained more than 7%. 

“US E&P stocks have struggled to start the year in 2023,” Leo Mariani, an analyst with Roth MKM, wrote in a research note Monday. “The real winners in our coverage are likely to be higher beta oil names.”

West Texas Intermediate crude was 6.3% higher at about $80 a barrel at 4:00 pm in New York. 

The energy sector is the best performer in the broader S&P 500 Monday with the top ten gainers in the benchmark all energy names. Marathon Oil Corp. and ConocoPhillips both rallied more than 9% while Hess Corp. surged 8.4%. APA Corp., Exxon Mobil and SLB were also among the market leaders. 

Canadian energy stocks were also lifted. International Petroleum Corp. rose 10%, helping to boost the S&P/TSX Composite index. Energy names lifted the country’s main stock index by 91.5 points on Monday. On an individual level, Canadian Natural Resources Ltd, the largest oil and gas producer listed in Toronto, provided the biggest boost, adding 35 points by itself.

Oil and gas tanker stocks, on the flip side, fell on expectations that the production cut would mean less crude to ship and higher fuel prices. Teekay Tankers Ltd. shed 9.4%, DHT Holdings Inc. fell 11.2% and International Seaways Inc. lost 6.6%. 

(Updates prices after market close)

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