UPDATE 1-Hellenic Petroleum Q1 net up 77 pct

(Adds details, CEO comment)

ATHENS, May 12 (Reuters) - Hellenic Petroleum (HEPr.AT: Quote, Profile, Research, Stock Buzz), Greece's largest refiner, said on Monday first-quarter net profit rose 77 percent year-on-year, as higher oil prices more than offset lower refining margins.

Net profit was 97 million euros ($150 million) on sales of 2.5 billion euros, which were up 35 percent.

The refiner said a 67 percent rise in crude oil prices in the first quarter and improved performance in its non-refining operations more than outweighed a decline in refinery margins due to the euro's strength against the dollar.

Earnings before interest, tax, depreciation and amortisation (EBITDA) rose 39 percent to 141 million euros, while "clean" EBITDA -- excluding inventory effects -- was down 4 percent to 96 million euros.

"This last quarter has been a challenging one, with rapidly rising crude oil prices reaching all time highs, a continuous weakening of the USD, low gasoline and fuel oil cracks and unprecedented volatility," Chief Executive John Costopoulos said in a statement.

He said it was difficult to give a full-year outlook given the volatile market conditions.

Hellenic Petroleum shares, which fell 2.79 percent to 9.76 euros on Monday, trade at about 13 times estimated 2008 earnings, slightly above Greek rival Motor Oil (MORr.AT: Quote, Profile, Research, Stock Buzz) on 12 times, according to Reuters Estimates.

The stock is down about 12 percent so far this year, outperforming the broader Greek market , which has lost some 18 percent, on prospects for improved refining margins boosting profit growth. (Reporting by Angeliki Koutantou; editing by Sue Thomas)