ExxonMobil Corp. (NYSE: XOM) and Chevron Corp. (NYSE: CVX) posted rare quarterly earnings misses Feb. 2 as cost cuts and rising oil prices failed to offset weakness in international refining operations, sending shares down in trading.

ExxonMobil’s stock dropped 5% as weaker than expected results from the world’s largest publicly-traded oil producer contrasted with improvements at European rivals. Chevron’s shares fell about 4%. Both companies are part of the Dow Jones Industrial Average, which was down 1%.

Even though oil prices jumped 25% in 2017 over the prior year, boosting the pair’s U.S. production operations, international refining and chemical profits struggled in the fourth quarter, fueling concerns that a weak spot could be emerging in the industry.

“It was a pair of disappointing results from both companies,” said Brian Youngberg, an oil industry analyst at Edward Jones. “Is refining something to be concerned about as we move through 2018? Will that be an offset to those higher oil prices?”

Both companies recorded gains from recent U.S. tax reform. Non-cash gains were $5.94 billion at ExxonMobil and $2 billion at Chevron.

Excluding that tax change and other one-time items, ExxonMobil earned 88 cents per share. By that measure, analysts expected earnings of $1.04 per share, according to Thomson Reuters I/B/E/S.

The earnings miss fueled more bad news for ExxonMobil, coming as rival Royal Dutch Shell, the world’s second-largest oil company, overtook ExxonMobil’s annual cash generation for the first time, producing about 6% more cash last year than ExxonMobil’s $33.2 billion in 2017.

ExxonMobil’s production fell 3% to 4 million barrels of oil equivalent per day, with the only output gains in the company's portfolio coming from the United States.

At Chevron, production rose, but excluding the tax change and other one-time items, the company earned 72 cents per share. By that measure, analysts expected earnings of $1.22 per share, according to Thomson Reuters I/B/E/S.

France’s Total SA and the United Kingdom’s BP Plc plan to post quarterly results later this month. BP has vowed to not change its spending plans because of rising global oil prices and only to approve projects that can make money with prices below $40 per barrel.