Schlumberger Ltd , the world's largest oilfield services company, reported a 36 percent rise in quarterly earnings, beating Wall Street forecasts, but it warned that Europe's debt crisis could hurt economic growth and trim oil demand.

The International Energy Agency cut its oil demand forecast earlier this week, saying the possibility of a credit crunch in Europe could set off a recession that would cut energy consumption.

Oilfield service companies have benefited from strong crude oil prices, which have prompted their energy-producing customers to hike spending by about 10 percent this year, according to a survey by Barclays Capital.

Schlumberger said in a statement that its planned capital spending would rise by more than 12 percent to nearly $4.5 billion this year, but added that it was building the required flexibility into our resource plans.

This is code for throttling back on spending, at a minimum, if warranted, Simmons & Co analyst Bill Herbert wrote in a note to investors.

Schlumberger said its growth in North America was driven by business in the deepwater Gulf of Mexico, where activity is increasing after the 2010 BP Plc oil spill brought drilling there to a standstill.

Offshore activity in Africa and land business in the Middle East and North Africa were also strong, the company said.

Still, recent price increases that had helped the onshore business in North America have slowed from the third quarter, according to Schlumberger.

U.S. drilling activity has exploded in recent years as the development of shale rock formations has surged. That has been a boon for Schlumberger and rival Halliburton Co , which reports its quarterly earnings next week.

That drilling has led to a glut of natural gas and pushed prices for the fuel to its lowest levels in a decade, raising expectations that such activity will decline.

Schlumberger's fourth-quarter net profit rose to $1.4 billion, or $1.05 per share, from $1.0 billion, or 76 cents per share, a year earlier.

Excluding one-time items, earnings per share of $1.11 topped the $1.09 that analysts had on average forecast, according to Thomson Reuters I/B/E/S.

Revenue rose about 21 percent to $11 billion, above the $10.8 billion analysts had expected.

Schlumberger shares were up 0.5 percent at $73.25 in premarket trading.

(Reporting by Matt Daily in New York, Krishna N Das in Bangalore and Braden Reddall in San Francisco; Editing by Lisa Von Ahn)