Glencore International Plc has revised the price range for its planned $11 billion initial public offering to 520-550 pence per share, from an earlier guidance of 480-580 pence each, a source with direct knowledge of the matter told Reuters on Monday.

Underwriters usually send out a new pricing guidance to reflect the range in which the offer has attracted maximum demand. The recent downturn in commodities markets has raised some doubt about whether the IPO will continue to attract the same demand. The new guidance indicates the company is not willing to sell shares at the bottom of the band as some investors will have hoped.

The new range lifts the mid-point of the offer to 535 pence, up from 530 pence.

Some European fund managers were betting that the rout in commodities markets would give institutional investors the pricing power on the IPO.

Glencore is set to close the IPO books on Tuesday, one day ahead of schedule, with final pricing due on May 19.

Order books for shares in Glencore, the world's largest diversified commodities trader, were fully covered within hours of the start of the sale process, but part of that success is a result of the relatively small stake in the company being placed with funds and because of Glencore's size, which makes it a must-buy for many.

Glencore has sold about a third of the offer to cornerstone investors, who have agreed to a six-month lock-up in return for a guaranteed allotment.

Chief Executive Ivan Glasenberg told reporters in Hong Kong last week that the IPO had generated strong demand, dismissing agitation in commodities markets as froth.

(Reporting by Fiona Lau; Writing by Denny Thomas; Editing by Chris Lewis)