The deal is expected to close in mid-2016 if approved by shareholders of both companies. The result would be the world's largest hotel company, with more than 30 leading hotel brands, 5,500 hotels and 1.1 million rooms worldwide, including franchise operations.
The acquisition also means that the Marriott Rewards program, which has 54 million members, and the Starwood Preferred Guest program, with 21 million members, will be blended.
And while Marriott CEO Arne Sorenson said the best of both programs would be preserved, travel experts predict change.
"There are a lot of mixed emotions about this," said Travel Skills founder Chris McGinnis.
"Starwood has done a very good job of taking very good care of its top customers via its generous SPG program. Since Marriott is going to be steering this ship, SPG members should brace for some tightening around perks and benefits."
The SPG program, explains Scott Mackenzie on the Travel Codex blog, is considered to be one of the most rewarding loyalty programs. "Points can be easily transferred to dozens of airlines, the value of these points is quite high for hotel redemptions …and status offers generous guaranteed benefits such as suite upgrades, with availability, and free breakfast," he said.
By contrast, Mackenzie notes that Marriott Rewards has more limited airline partnerships, relatively high elite qualification requirements and numerous exceptions to its benefits.
"Marriott does treat its top-tier platinum guests to nicer rooms but rarely gives them suites," the Associated Press reported. "Both programs offer free breakfast to platinum members, except Marriott doesn't do so at its Courtyard hotels or at resorts."
Members of Marriott Rewards say they value the program "because wherever they go they can earn their points, and because of the consistency," writes Gary Leff on the View from the Wing blog, "However no Starwood Platinum ever said to themselves they'd rather be a Marriott Platinum.""Starwood has done a very good job of taking very good care of its top customers via its generous SPG program. Since Marriott is going to be steering this ship, SPG members should brace for some tightening around perks and benefits."
"For now, there's no need for Starwood members to panic," said John DiScala of JohnnyJet.com. No details have been released on changes in the programs and nothing can change until the deal closes, sometime next year.
"But start thinking about where to transfer your SPG points," he advises, referring to airline miles, gift cards or other services
Experts note, however, that the Marriott - Starwood merger also offers travelers some upsides.
"Members of both programs will have lots of new opportunities to earn points," said McGinnis, "And Marriott's staid product range will get a shot of Starwood's well-honed glamour."
Starwood's brands include St. Regis, The Luxury Collection, W, Design Hotels, Le Meridien, Sheraton, Four Points by Sheraton, Aloft, Element, the new Tribute Portfolio and Westin, which is opening a new hotel at Denver International Airport this week.
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Marriott's 16 brands include the Marriott, JW Marriott and Renaissance Hotels & Resorts, EDITION Hotels, the Autograph Collection, Courtyard, Residence Inn, Fairfield Inn, Springhill Suites, The Ritz-Carlton and others.