Halliburton Co , the world's second-largest oilfield services company, posted better-than-expected first-quarter earnings, lifted by a three-fold jump in profits at its key North American operations.

Oil companies have increased spending on new projects to take advantage of high oil prices, which surged above $100 per barrel in late February and have remained strong due to turmoil in the Middle East and fears about the global economic recovery.

The unrest in Libya prompted the United Nations to impose economic sanctions on the North African country, forcing Halliburton and other energy companies to pull out, and Halliburton said it took a $46 million charge in the quarter.

Halliburton's net profit rose to $511 million, or 56 cents per share, from $206 million, or 23 cents per share, a year earlier.

Excluding the charge from its operations in Libya, the company earned 61 cents per share, topping the 58 cents per share that analysts had forecast on average, according to Thomson Reuters I/B/E/S.

Revenue rose to $5.3 billion, also better than analysts' forecasts for $4.89 billion.

We expect our Eastern Hemisphere margins to improve in the second quarter but they will continue to be impacted by the situation in Libya and by competitive pricing, Chief Executive Dave Lesar said in a statement.

Larger rival Schlumberger Ltd will post its results on Thursday along with Weatherford International Ltd , while Baker Hughes Inc reports on April 27.

Halliburton shares are up 15 percent since the start of 2011, in line with the Philadelphia Stock Exchange oil service index <.OSX>, but better than Schlumberger's 4 percent gain.

Its shares rose less than 1 percent in premarket trading.

(Additional reporting by Braden Reddall in San Francisco, editing by Maureen Bavdek)