eMarketer, PhoCusWright, Forrester Research and comScore Networks all agree that online travel sales growth is declining. And slowing growth is not the only problem.

"The travel industry is undergoing a revolution that is redefining the rules of engagement between travel firms and consumers," says Jeffrey Grau, Senior Analyst and the author of the new US Online Travel: The Threat of Commoditization report. "In addition, a tighter market will exacerbate the fierce competition between online travel agencies and travel suppliers in an already commoditized market."

In other words, tighten your seat belts.

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