HOUSTON (Reuters) - Exxon Mobil Corp and Chevron Corp posted rare quarterly earnings misses on Friday as cost cuts and rising oil prices failed to offset weakness in international refining operations, sending shares of both companies plunging.

The results surprised Wall Street, where analysts had been steadily raising expectations due to stronger crude prices and a rebounding global economy, according to Thomson Reuters data.

But excluding U.S. tax benefits, results at both companies fell short of expectations, casting a cloud over the U.S. oil industry just days after the nation’s output surpassed a milestone 10 million barrels per day.

“We got carried away with our expectations, and by we, I mean Wall Street as a whole,” said Oliver Pursche of wealth manager Bruderman Brothers LLC, which holds Exxon shares.

Exxon, Chevron and rival Royal Dutch Shell all reported lower cash flow from operations in the fourth quarter despite higher oil and gas prices. Reasons varied, but included weaker refining profits and spending on capital expenses.

Shell, the world’s second-largest publicly traded oil company after Exxon, managed to overtake its bigger rival for the first time in a key area, producing about 6 percent more cash last year than Exxon’s $33.2 billion.

“What struck us the most was the decline in cash flow from operations at Exxon,” Pursche said.

A logo of Exxon Mobil is displayed on a monitor above the floor of the New York Stock Exchange shortly after the opening bell in New York, U.S., December 5, 2017. REUTERS/Lucas Jackson

Exxon’s stock dropped 6 percent in Friday afternoon trading, the biggest one-day drop since August 2011. The stock had been making gains after hitting a low last summer, closing Thursday at a 52-week high. But Exxon shares are flat over the past year despite a 22 percent rise in the S&P 500.

Analysts needled Exxon’s director of investor relations, Jeff Woodbury, with unusually pointed questions about the cash flow drop on a Friday earnings conference call. Exxon Chief Executive Darren Woods did not participate in the call.

The frustration boiled over into the Chevron call, which followed Exxon’s. Mike Wirth, in his second day as Chevron’s CEO, described the refining weakness a one-time issue rather than a systemic problem.

While Wirth’s answers did not seem to mollify all analysts, several thanked him for talking. “I really appreciate you coming on the call from time to time,” Barclays Capital analyst Paul Cheng said to Wirth. “I hope that at least one of your other major competitors will do the same.”

Chevron’s shares were off more than 5 percent in afternoon trading. Both companies are part of the Dow Jones Industrial Average, which fell more than 2 percent in late trading.

“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?”

Chevron said higher oil prices, up 25 percent in 2017, and currency impacts hurt refining margins by $500 million in the quarter.

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

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

Exxon’s quarterly production fell 3 percent to 4 million barrels of oil equivalent per day, with the only gain coming from the United States. But its U.S. production business was unprofitable for the third year in a row.

At Chevron, production rose 2.6 percent. 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.

“I expect us to maintain capital cost and discipline,” Wirth said. “I intend to lead Chevron to win in any environment.”

France’s Total SA and the United Kingdom’s BP Plc plan to post quarterly results later this month.