By Sarah Young and Kate Holton
LONDON (Reuters) - Royal Dutch Shell
Analysts and investors had not considered van Beurden, who has worked for the company for 30 years, as a possible contender to replace Voser next year.
Their early focus was on Finance Director Simon Henry and other divisional heads Marvin Odum, Matthias Bichseland and Andrew Brown.
Voser, who built the oil company into a leader in liquefied natural gas (LNG) and was finance director at the company before taking the helm in 2009, shocked the industry by announcing his early departure over two months ago.
Shares in Shell gained 1 percent in early trading on Tuesday following the appointment of the relatively unknown van Beurden, who only joined the company's executive committee in January.
"It's initially something of a surprise. The question is, who is this guy," Royal Bank of Canada analyst Peter Hutton said.
Shell said van Beurden, a 55-year-old Dutchman, had a deep knowledge of the industry, having worked across a range of businesses and countries since he joined the firm in 1983.
"Ben will continue to drive and further develop the strategic agenda that we have set out, to generate competitive returns for our shareholders," said Chairman Jorma Ollila.
Van Beurden, whose new job will start next January, has worked in both the upstream and downstream parts of the company including within the increasingly important LNG business for 10 years.
His appointment comes as the company and its industry face huge challenges.
Shell is the western world's number two company by production behind Exxon Mobil
Amongst the other candidates who had been tipped as possible replacements for Voser were the company's head of upstream operations in the Americas, Marvin Odum, director of projects and technology Matthias Bichseland and Andrew Brown, who became head of international upstream last year.
RBC's Hutton pointed out that while the appointment of van Beurden was a surprise, Shell had in the past named bosses from the downstream, or refining, part of the business including Voser's predecessor Jeroen van der Veer.
He oversaw the initial stages of a recovery at Shell, which a decade ago was engulfed by crisis following a dramatic downgrade of reserves which rocked investor confidence when it became public in 2004.
Van Beurden, a chemical engineering graduate, has first-hand experience of the reserves crisis. He worked at the time as management assistant to Phil Watts, the CEO who was sacked as a result.
"He was clearly a high-flyer then and I am not surprised at all that he's made it all the way to the top," said a former colleague who no longer works for Shell.
(Additional reporting by Andrew Callus; Editing by Erica Billingham)