Priceline Group Inc. agreed to buy restaurant booking service OpenTable Inc. for about $2.6 billion in cash, broadening the online travel giant's offerings into a new field as some of its more established brands mature.

Priceline offered $103 a share in cash for the company, a 46% premium over its closing price Thursday. The deal is expected to close in the third quarter. OpenTable charges restaurants fees to book diners on top of monthly fees to use its software.

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