* Voser helped Shell recover from 2004 reserves crisis
* He goes as industry faces cost squeeze, price falls
* Shell looking at both external and internal candidates
* CFO Henry, U.S. upstream boss Odum possible contenders
* Shell joins peers in beating Q1 earnings forecasts
Royal Dutch Shell chief executive Peter Voser, who built the oil company into a leader in liquefied natural gas after a reserves accounting scandal, is to retire next year in a shock early departure.
The softly spoken and widely respected 54-year old Swiss national took over as finance chief in 2004 amid the board-level upheaval that followed Shell's dramatic downgrade of reserves estimates, becoming CEO in 2009.
His exit from a role he is seen to have excelled in surprised investors, analysts and people inside Europe's biggest oil company. Two senior members of staff told Reuters they had no inkling that he would go.
Voser said the move was driven by a desire for a change of lifestyle.
His departure, scheduled for the first half of next year and announced along with first-quarter results, comes as the company and its industry face huge challenges.
Shell is the western world's number two company by production behind Exxon Mobil. But, like its peers, it is struggling to replace reserves and boost production, and faces a squeeze on earnings as costs rise while the price of oil threatens to fall decisively below the psychologically important $100 a barrel level.
Shell said it would look outside and inside the company for Voser's replacement. However, as with most big oil companies, new chief executives traditionally come up through the ranks.
Finance director Simon Henry refused to be drawn on his prospects for succeeding Voser.
Inside Shell, Henry is regarded as a potential front-runner along with Marvin Odum, the company's head of upstream operations in the Americas.
Henry has a mathematics and accounting background even though, like Odum, he joined the company as an engineer, and is respected by shareholders who know him from his days as head of investor relations. Odum, who is about Voser's age, would be Shell's first American CEO.
Andrew Brown, who became head of international upstream last year, could be a candidate too, as could director of projects and technology Matthias Bichsel. One source said Brown's relatively recent appointment may make him an outside bet, while Bichsel, born in 1954, might be considered too old for the job.
Voser said his decision to go was a personal one.
"After such an exciting executive career I feel it is time for a change in my lifestyle and I am looking forward to having more time available for my family and private life in the years to come," he said in a statement.
He has been named in media reports as a possible future chairman of Roche Holding, the drug firm based in his native Switzerland at which he is already non-executive director.
But Henry said Voser had indicated he had no plans to take on new non-executive directorships or chairmanships.
STRONG TRADING, LIKE BP
The last of the western world's four biggest oil companies to report results, Shell joined its peers on Thursday in delivering a first-quarter profit that topped market expectations.
Henry said the company was well-placed to deal with the recent fall in oil prices.
"We also think there are quite few players in the market, quite a few companies, who actually have bet the farm on $100-plus oil prices. We don't," he said.
Nevertheless, analysts say that among the world's top oil companies, Shell spends more on exploration per barrel produced than any of its competitors. Its most high-profile exploration failure has been in Alaska, where it has spent $5 billion since 2006, and has yet to drill a single complete hole.
Adjusted net profit on a current cost of supply basis rose to $7.5 billion from $7.3 billion a year ago, compared with expectations of around $6.5 billion.
As was the case with BP's results on Tuesday, Shell exceeded expectations by a big margin thanks in large part to its trading activities, which were not split out from the rest of its operations.