UPDATE 4-US Steel buying oilfield equipment maker Lone Star

(Updates with price comparison, U.S. Steel tubular sales)

By Matt Daily and Steve James

NEW YORK, March 29 (Reuters) - U.S. Steel Corp. (X.N: Quote, Profile, Research, Stock Buzz) expanded its reach in the lucrative oilfield sector on Thursday with a $2.1 billion deal to buy Lone Star Technologies Inc. LSS.N, which makes products to line oil and gas wells and build pipelines.

"This is a very important strategic transaction," said U.S Steel Chairman and Chief Executive Officer John Surma. "With high energy price forecasts, tubular product demand should remain robust."

He also told Wall Street analysts on a conference call that the Lone Star deal is expected to boost the steelmaker's earnings this year and result in synergies of more than $100 million by the end of 2008.

In addition, said Surma, it widens U.S. Steel's geographic spread, since Lone Star has a pending joint venture in China, another in place in Brazil, and "is in discussions with a company in India."

The deal comes just six weeks after Tenaris SA (TS.N: Quote, Profile, Research, Stock Buzz) (TENR.MI: Quote, Profile, Research, Stock Buzz), the world's leading maker of tubular products for the oil and gas industry, agreed to buy Hydril Co. HYDL.O for $2.16 billion.

That was Tenaris' second U.S. purchase in less than a year, following the acquisition of Maverick Tube Corp. It highlights how oil at over $60 per barrel and high gas prices are attracting investment in the oilfield sector.

The latest deal calls for Pittsburgh-based U.S. Steel, which last year said it had considered a possible sale of its tubular business, to pay $67.50 per share of Lone Star -- a 39-percent premium to its Wednesday closing price.