ExxonMobil, the world's largest publicly traded oil company, posted lower-than-expected quarterly earnings on Thursday as its oil and gas output sagged and its chemicals business struggled.

Weaker global oil prices have weighed on earnings across the sector, and Exxon also felt the sting of decade-low U.S. natural gas prices.

The company, which has pledged to spend a record $37 billion this year as it brings new projects on line, said oil and gas output fell 5.6% to 4.15 million barrels oil equivalent per day during the quarter.

"Production was a little light," Pavel Molchanov, analyst at Raymond James, said. "The real swing versus our estimates was chemicals."

The Irving, Texas, company reported a second-quarter profit of $15.9 billion, or $3.41 per share, up from $10.68 billion, or $2.18 per share, a year earlier.

Profit was boosted by a $7.5 billion gain related to the sale of a stake in its Japanese refining and chemicals business, and tax items.

Excluding those one-time gains, Exxon earned $8.4 billion, or $1.80 per share. On that basis, analysts' average forecast was $1.95, according to Thomson Reuters I/B/E/S.

Excluding one-time items, earnings from the company's chemical operations totaled $820 million, nearly 33% below Raymond James' estimate for the unit, Molchanov said.

Weakness in the chemicals market was also evident in the earnings of Dow Chemical, which reported a 34% drop in quarterly profit, missing Wall Street forecasts.

Earlier on Thursday, Royal Dutch Shell posted lower-than-expected quarterly earnings of $5.7 billion, hurt by maintenance costs and shutdowns in the U.S. Gulf, where the company has some of its most profitable production, and in Australian Liquefied Natural Gas.

Exxon's earnings from U.S. oil and gas production tumbled by more than half in the second quarter to $678 million, largely due to the steep decline in prices of natural gas.

The company is the nation's largest producer of natural gas, but Chief Executive Officer Rex Tillerson warned last month that prices were too low to allow the industry to cover the cost of finding and producing new supply.

"We are all losing our shirts today," Tillerson said at the time.