Schlumberger Ltd , the world's largest oilfield services company, posted a lower-than-expected third-quarter profit and said financial turmoil had cut oil demand, sending its shares lower in pre-market trading.

Oil prices have fallen from their second-quarter peak, raising concerns that energy companies would trim spending on new wells.

Despite that weaker oil price, Schlumberger said offshore demand would help its business, which was boosted by growth in Iraq, Saudi Arabia, Mexico and Brazil in the third quarter.

While the financial turmoil introduces some uncertainty over near-term activity, we remain confident that any reductions will be short-lived, and that the outlook for the service industry remains very positive, Paal Kibsgaard, Schlumberger's new chief executive said in a statement.

Schlumberger's profits were hurt by a weaker-than-expected results from the Middle East, where its Western Geco business suffered, according to Angie Sedita, analyst at UBS.

But profits in North America topped expectations, driven by brisk demand from oil companies who continue to drill aggressively in the region's lucrative shale fields.

Third-quarter net profit fell to $1.3 billion, or 96 cents a share, from $1.7 billion, or $1.38 cents a share, a year earlier, when the company recorded a gain of nearly $1 per share due to the increased value of M-I Swaco after Schlumberger bought Smith, its partner in the joint venture.

Excluding one-time items, Schlumberger earned 98 cents per share, compared with the analysts' average forecast of $1.01, according to Thomson Reuters I/B/E/S.

Schlumberger said on Friday its third-quarter revenue rose 49 percent to $10.23 billion, in line with analysts' forecasts.

The quarter also included a handover of the chief executive mantle to 44-year-old Kibsgaard from Andrew Gould, a closely followed industry figure who is still Schlumberger's chairman.

On Monday, Schlumberger's rival Halliburton Co said growth outside North America helped it post better-than-expected quarterly profit, but Halliburton's less assured view of North American prospects led investors to hammer down its shares.

As of Thursday's close, Schlumberger's shares were down 23 percent in the past six months, while Halliburton has tumbled 31 percent, both tracking the oilfield services sector lower in response to sliding oil prices.

In pre-market trading on Friday, the shares slipped 3.3 percent to $65.74 per share.

(Reporting by Matt Daily; Additional reporting by Braden Reddall; Editing by Lisa Von Ahn and Derek Caney)

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