Exxon Mobil Corp disappointed investors who in the past week had grown accustomed to energy companies reporting better-than-expected profits despite the collapse in crude oil prices since July.

British gas producer BG Group Plc earlier on Thursday reported a smaller-than-expected drop in first-quarter profit, just as BP Plc and Royal Dutch Shell Plc did this week and ConocoPhillips did last week.

But Exxon, the world's largest listed company and the oil sector leader, said Thursday that profit fell 58 percent to $4.55 billion, missing forecasts.

Exxon shares fell 2.0 percent while shares of Marathon Oil Corp , which also reported earnings short of estimates, fell 2.3 percent. Other U.S. oil companies dropped in sympathy.

Mark Coffelt, head portfolio manager at Empiric Advisors in Austin, Texas, said Exxon offered a glimpse of what to expect generally from Chevron Corp when it reports on Friday.

I think they probably stack up pretty similarly, he said, adding that none of them could avoid the $100 drop in the price of a barrel of oil since July to about $50 now.

Apache Corp , currently the top U.S. independent oil and natural gas producer by value, reported better-than-expected operating earnings, but had to take a $2 billion writedown due to a collapse in natural gas prices.

Exxon and BG's core oil and gas production units suffered big profit falls due to lower prices. BG's performance was compounded by a 5 percent fall in oil and gas production, while Exxon said output rose 2 percent to 4.2 million barrels of oil equivalent per day.

International upstream (exploration and production) did not see the level of cost reduction that some of the other oil companies did, Jason Gammel, oil analyst at Macquarie Research, said of Exxon.

BG's first-quarter profit, excluding one-time items, fell 13 percent to 690 million pounds ($1 billion), but was ahead of a forecast of 613 million pounds from a Reuters Estimates analysts poll. BG shares rose 1.5 percent.

Its relatively strong results were largely driven by a big jump in profits from shipping liquefied natural gas around the world.

BG Group's integrated gas business is reflected in the distinctive resilience of our profits and cash flow in this challenging economic environment, Chief Executive Frank Chapman said in a statement.

Analysts agreed.

BG's strategy to hedge and protect its LNG profits has paid off, said Richard Griffith, analyst at Evolution Securities.

As for companies that serve the producers, Norwegian oil industry suppliers Aker Solutions ASA and Fred. Olsen Energy posted bigger-than-expected profit rises, despite investors' fears that the oil services sector would be hardest hit by the drop in oil prices.

France's Technip , which builds oil rigs and deepwater pipelines, also reported a forecast-beating rise in first-quarter profit and confirmed its 2009 outlook.

(Additional reporting by Wojciech Moskwa in Oslo, Matt Daily in New York, Anna Driver in Houston; Editing by Jon Loades-Carter, Rupert Winchester and Gerald E. McCormick)

Energy