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Priceline Group, the online travel booking service best known for its quirky ads featuring actor William Shatner, said Friday it has agreed to buy online restaurant-reservation service OpenTable.com for $2.6 billion in cash.

The boards of directors of both companies have approved the deal, which is expected to close in the third quarter subject to regulatory clearances, the companies said. At $103 per share, the purchase price represents a 46 percent premium over the closing price of OpenTable’s stock at the end of trading Thursday.

Founded in 1997, Norwalk, Conn.-based Priceline says it books more than 1 million guests per day in 480,000 properties in 200 countries. With the OpenTable acquisition, the company is adding restaurant reservations to a portfolio of travel- and lodging-focused properties that already includes Booking.com, KAYAK.com, Agoda.com in Asia and RentalCars.com.

In May, Priceline announced that its first-quarter gross profit had increased 39 percent compared to the prior year, an uptick driven largely by international bookings.

San Francisco-based OpenTable, which was founded in 1998, says it helps some 15,000 diners per month make reservations in more than 31,000 restaurants. The company will continue to operate independently under its current management and in its existing headquarters, Priceline said.

“OpenTable is a great match for The Priceline Group. They provide us with a natural extension into restaurant marketing services and a wonderful and highly valued booking experience for our global customers,” Priceline Group president and CEO Darren Huston said in a company news release.

In his own statement, OpenTable CEO Matt Roberts said, “The Priceline Group is a leader in e-commerce innovation with global expertise in online marketing and digital customer conversion across devices, and they have an exceptional track record of customer service in dozens of languages around the world.”

Sullivan & Cromwell is advising Priceline in connection with the OpenTable acquisition. The firm’s team includes corporate partners Keith Pagnani and Brian Hamilton; tax partner Ronald Creamer, Jr.; intellectual property counsel Spencer Simon; executive compensation and benefits partner Matthew Friestedt; and antitrust partner Steven Holley, all of whom are based in New York. London-based antitrust partner Juan Rodriguez is also advising.

The Sullivan & Cromwell associates working on the matter are Mimi Butler, Georg Krause-Vilmar and Andrew Rocks, all in New York.

Executive vice president and general counsel Peter Millones and senior vice president and associate general counsel Steve Sonne made up Priceline’s in-house legal team.

Sullivan & Cromwell also represented Priceline.com when it acquired rival KAYAK in a $1.8 billion deal announced in 2012.

For its part, OpenTable is being represented by a Latham & Watkins team led by Silicon Valley-based Patrick Pohlen, cochair of the firm’s emerging company practice, and corporate partner Luke Bergstrom, along with corporate partner Kathleen Wells, cochair of the corporate department in Silicon Valley. The other Latham attorneys working on the deal include tax partner Grace Chen, employee benefits partner Jay Metz, intellectual property partner JD Marple and antitrust partners Karen Silverman and Joshua Holian.

Rounding out the Latham team are associates Una Au, Heather Bromfield, Julie Crisp, William Hackett, Corinna Liebowitz, Chad Rolston, Arielle Singh and Matthew Van Leeuwen. Au, Chen, Crisp, Hackett, Holian and Silverman are based in San Francisco; the other associates work out of the Silicon Valley office.

Latham advised OpenTable on its initial public offering in May 2009 and has represented the company in connection with a number of acquisitions since then, including its September 2010 purchase of toptable.com, a restaurant reservation site in the United Kingdom, the firm said.

John Orta is OpenTable’s senior vice president and general counsel.

Shearman & Sterling also had a hand in the matter, advising Qatalyst Partners in connection with its role as OpenTable’s financial adviser. The Shearman team includes mergers and acquisitions partner Steve Camahort and associate Lisa Lopshire, both in San Francisco, the firm said.