Interpublic Group's Wenham, Mass.-based Mullen beat Omnicom Group's Element 79, Chicago, in a review for the travel website's account formerly held by WPP Group's Young & Rubicam, Chicago.

The move comes as Orbitz appears to be taking market share away from rivals Travelocity, Expedia and Priceline, writes AdAge. Domestic gross bookings were up 30 percent in the first quarter and 43 percent in the second quarter - and are expected to increase to around 30 percent for the third quarter.

The online-booking sector is becoming increasingly competitive: Expedia and Travelocity have boosted spending; travel-search aggregators such as Kayak and Sidestep have begun offering similar services; American Express recently announced plans for its own online-booking service; and the five major airlines that founded Orbitz in 2001 have seen traffic on their own websites climb.

Orbitz President Steven Barnhart, who took office in September, a few months after the sale of website to private-equity firm the Blackstone Group, said in an October interview with Crain's Chicago Business that his plan to grow Orbitz included upgrading overall marketing.