Shell CEO keeps oil sands options open, touts gas

* Says faster expansion in oil sands still possible

* Costs remain a concern

* Sees growing gas demand from emerging economies (In U.S. dollars)

MONTREAL, Quebec, Sept 13 (Reuters) - Royal Dutch Shell Plc (RDSa.L: Quote) could switch away from its slow-growth strategy in Canada's oil sands but costs in the region remain a concern, the company's chief executive said on Monday.

Shell, which operates the 155,000 barrel-per-day Athabasca oil sands mine and upgrader in northern Alberta, has nearly wrapped up a 100,000 bpd expansion of the project.

However it stepped back from plans for a further series of big expansions of its oil sands holdings after a squeezed labor pool in northern Alberta inflated construction costs and oil prices fell following the economic crisis.

Instead of big-ticket expansions, Shell Chief Executive Peter Voser steered the European oil major to smaller projects, looking to increase output in 30,000 bpd increments by tweaking operations at its two oil sands mines.

But Voser said that the alternative strategy of expanding oil sands output more and faster remains a possibility, though he's uninterested in stoking further inflation.

"We left it open to go back to a more aggressive expansion if that is needed and if that actually is possible because of the costs," Voser told reporters at the World Energy Congress in Montreal.