HOUSTON -- The global oil and gas supermajors struggled to improve profitability in the third quarter despite strong crude oil prices and a good refining business environment.

Concern over weaker business performances by the oil and gas giants first sprouted after Chevron announced last month that its investors should expect third-quarter earnings to be "substantially lower than second quarter 2012." Chevron announces its final third-quarter results today.

Those worries were more or less substantiated after major companies posted their numbers this week.

The exception was BP PLC, which seems on track to recover from the steep decline in earnings resulting from the 2010 Macondo offshore oil spill in the Gulf of Mexico. Earlier this week, BP told investors that its earnings were strong compared with the previous three months of the year, though the figure was down somewhat from the same period of 2011.

But yesterday Exxon Mobil Corp. and Royal Dutch Shell PLC reported flat to lower third-quarter 2012 earnings. Good profitability from downstream refining and marketing businesses helped, but not enough to offset lost hydrocarbon production and slightly weaker average commodities prices compared with last year.

Exxon Mobil reported third-quarter earnings of $9.6 billion, $760 million less than in the third quarter of 2011, representing a 7 percent slide. But so far the company seems set to clock in much higher profits for all of 2012 than in the prior year -- Exxon Mobil said earnings are up 10 percent over 2011 when counting the first nine months of both years.

Total earnings reported by Exxon Mobil so far this year have reached nearly $35 billion.

"Global economic uncertainty continued in the third quarter" and contributed to the 7 percent year-over-year decline, said Exxon Mobil's vice president for investor relations, David Rosenthal. He cited weak economies in the European Union and Japan as one factor behind the flat earnings, though his company believes the United States' economy "marginally improved versus the second quarter."

Despite a slump compared with the third quarter of 2011, Rosenthal said investors have reason to be optimistic about his company's prospects in the coming months and years.

A major project in Nigeria, the Satellites Phase 1 development, should produce first oil before the end of the year, the company announced. Exxon Mobil also sees promising new developments in the U.S. Gulf of Mexico deepwater offshore environment and holds major stakes in offshore Black Sea blocks. The company also expects a major liquefied natural gas (LNG) export project in Papua New Guinea to come online by 2014.

Exxon Mobil's overall financial health is sound, Rosenthal said.

"Our cash generation remains strong, with $14 billion in cash flows from operations and asset sales," he said. Higher margins from refining operations helped offset somewhat lower profits from exploration and production, Rosenthal added. "Downstream earnings improved by $1.6 billion."

Shell earnings fall on economic woes

The picture was largely similar at Shell, which also posted its quarterly financial results yesterday.

Earnings on a "current cost of supplies" basis came in at $6.1 billion, down from $7.2 billion in the third quarter of 2011, about a 15.3 percent decline.

Shell's earnings over a nine-month period fell by 11 percent, from $22.2 billion in 2011 to $19.75 billion over the first three quarters of this year. But the company reported strong cash flow growth, rising 20 percent over a nine-month basis, from about $30 billion last year to $36 billion.

Shell CEO Peter Voser told investors and analysts that the drop in earnings was attributed to lower oil and gas prices and softening profits from chemical sales, all a result of a struggling international economy.

Good profits from refining operations helped shore up Shell's financial performance somewhat. But in a conference call, Shell Chief Financial Officer Simon Henry warned that his company thinks the better business environment for refining was largely due to disruptions in supply, primarily caused by a major refining center fire in Venezuela and disrupted manufacturing along the Gulf of Mexico as a result of Hurricane Isaac.

Isaac also contributed to a decline in Shell's global hydrocarbons production for the third quarter. Henry put production figures at about 3 million barrels of oil equivalent per day during the period, down by around 26,000 boe per day, a drop caused mainly by the forced shut-in of offshore operations as the storm entered the central Gulf. Other production declines were partly a result of Shell's $6 billion in asset sales.

Henry promised shareholders better days to come for Shell.

"We've launched new oil and gas projects in Italy and the U.K., and we've been adding new positions for future growth," he said.

Especially promising, Henry said, is the rise of Shell's massive gas-to-liquids project in Qatar. LNG production in Qatar has also risen by around 4 percent and the company is closing in on running at full capacity at that site, with both trains already at around 95 percent utilization, Henry reported.

Bright spot for BP

Compared with its peers in the industry, oil and gas giant BP has been faring better.

On Tuesday, the company said its earnings grew by 40 percent over the previous three months of the year, from $3.7 billion in the second quarter of 2012 to $5.2 billion in the third quarter. Earnings dipped from the $5.5 billion the company announced in the third quarter of last year, but BP says that drop doesn't factor in some major asset divestments that softened the company's cash flow compared with last year.

The company credited the jump to a "strong performance in BP's downstream business, where good operational delivery capitalized on increased refining margins." Average daily hydrocarbon production stayed flat compared with the same period last year, at about 2.26 million boe per day. Growing oil and gas output from new projects was offset by cuts to production forced by maintenance work in Alaska and the North Sea, the company said.

BP also announced this week that it will finish paying into a Gulf of Mexico Trust Fund set up after the 2010 oil spill by the end of this year. A final installment of $860 million into the $20 billion fund will be paid in the fourth quarter, BP said.