Over the last year the biggest oil companies have shown the most resilience in the face of plunging oil prices. But now even the likes of Exxon Mobil, BP and Chevron are beginning to lose their buoyancy.

The newest measure of the oil industry’s falling fortunes came on Tuesday in the form of a $3.3 billion fourth-quarter loss reported by BP. Exxon Mobil, the American industry’s largest player, reported a 58 percent decline in its quarterly profit.

Low oil and natural gas prices are saving families hundreds of dollars a year, but there are few cheers among energy executives. The entire industry is reeling from the effects of a global glut, and slackening international economic growth.

Any prospect that big global producers like Saudi Arabia and Russia will cut production to reverse the 70 percent drop in oil prices over the last 18 months has been squashed in recent weeks. Iran has promised to add another 500,000 barrels a day to the world market now that several sanctions have been lifted after the recent nuclear deal.

Global production exceeds demand by more than one million barrels a day, and storage space is running out. Longer term, there are questions about the value of oil still underground, as climate concerns prompt energy users of all sizes to seek alternatives to fossil fuels.

This is the worst industry decline since similar commodity price collapses in the 1980s and 1990s forced oil companies to slash payrolls and dividends, although the biggest companies have generally fared far better than the smaller independents. BP and Exxon Mobil continue to pledge their commitment to their dividends, helped by the strong returns that refineries tend to show when oil and gas, vital raw inputs, are low.

Senior oil executives noted that unseasonably warm weather had lowered demand for natural gas and that refining and chemical profit margins were weakening in some areas of the world. But despite the challenges, oil executives on Tuesday expressed confidence that their businesses would survive and prosper in the future, and that oil and gas prices would eventually rebound.

“For both gas and oil we are constructive on long-term demand growth,” Jeffrey J. Woodbury, Exxon Mobil’s vice president for investor relations, said in a conference call.

Speaking to reporters in London, Bob Dudley, BP’s chief executive, forecast that demand for oil would most likely catch up with falling output in the second half of this year, leading to an easing of the glut that has depressed prices.

“As these start working together — the supply and demand fundamentals,” Mr. Dudley said, “you can characterize the price as lower for longer but it’s not lower forever.”

Nevertheless, as oil prices slumped again on Tuesday by about 5 percent, Exxon Mobil shares were down 2.2 percent and BP shares shed 8.5 percent of their value. The American benchmark oil price broke just under $30 a barrel, a level that makes drilling unprofitable almost everywhere in the United States.

Exxon Mobil’s profit of $2.78 billion was down from $6.57 billion the year before. Its exploration and production business lost $538 million in the United States, though its total global upstream earnings for the quarter were $857 million.

For all of 2015, the company’s net income of $16.2 billion was roughly half that of 2014.

The results would have been far worse had it not been for the company’s refining and chemical businesses. It had refining and marketing earnings of $1.35 billion, up from $497 million the year before. With the price of oil near $30 a barrel, the company said it would pare share repurchases as a cost-saving measure.

“We have built this business to ensure it is durable in a low-price environment,” Mr. Woodbury said.

For all of 2015, BP said it lost $6.48 billion, compared with a profit of $3.78 billion in 2014 — before plummeting oil prices began taking their full toll.

On Tuesday, BP repeated a commitment it made last month to cut 4,000 jobs this year in its exploration and production unit, which lost $728 million in the quarter. BP also said it would trim about 3,000 workers from its marketing and refining business by the end of 2017. Before those cuts, BP had a global work force of about 80,000.

The company also said it wrote down the value of its oil and gas assets by $1.6 billion in the quarter in response to plunging prices.

Hoping to keep more investors from fleeing, BP said on Tuesday that despite its financial losses it would keep its dividend unchanged.

BP has sought to streamline its operations by selling some businesses — a strategy in some ways forced by its need to raise money to help pay damages from its oil well blowout in the Gulf of Mexico in 2010. The company took a charge of $443 million in the fourth quarter for that spill, bringing total provisions for the disaster to $55.5 billion.

Since 2010, the company has raised about $60 billion through sales of assets including stakes in three large Gulf of Mexico oil fields in 2012 and a Texas refinery in 2013. Most of those sales were made when oil prices were much higher than today. Other companies are finding it hard to find buyers for businesses or operations they might want to sell.

The American oil giant Chevron, for example, cited that problem last week when it reported its first quarterly loss since 2002.

“It is a terrible market to be trying to sell most assets out there,” John S. Watson, the chairman and chief executive of Chevron, said on Friday during a conference call with analysts.

Chevron lost $588 million in the last quarter of 2015, compared with a $3.5 billion profit in the period a year earlier.