HOUSTON (Reuters) - Marathon Oil Corp <MRO.N> said on Thursday first-quarter earnings edged up 2 percent, surpassing Wall Street estimates, as profits from record oil prices outweighed weak margins at its refining business.

Benchmark U.S. oil prices averaged a record of close to $98 a barrel during the quarter, up nearly 70 percent from a year earlier, but refiners struggled to push through the full price increase to customers.

Net income rose to $731 million from $717 million a year earlier. Earnings per share fell by a penny, to $1.02, because of an increase in shares outstanding.

Adjusted for special items, earnings were $1.07 per share, well above analysts' average forecast of 82 cents, according to Reuters Estimates.

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Planned maintenance at two refineries hurt downstream margins, the Houston-based company said.

Income at Marathon's exploration and production unit climbed 78 percent to $684 million due to higher liquid hydrocarbon prices.

The company's refining, marketing and transportation unit reported a loss of $75 million, compared with a profit of $345 million a year earlier.

Shares of Marathon climbed 2 percent, or 92 cents, to $46.49 in morning trading on the New York Stock Exchange.

(Reporting by Anna Driver; editing by John Wallace)