Orange said four-year-old OpenX had the scale and maturity to compete with giants such as Google, Yahoo or AOL, and was more suited to its cross-media advertising strategy spanning mobile and television.
Los Angeles-based OpenX, which is backed by Accel Partners and Index Ventures, already has a separate partnership with Orange, the key brand of France Telecom, for an online advertising buying and selling platform in Europe.
"We are switching all our countries from DoubleClick to OpenX," said a senior France Telecom manager who asked not to be named. Orange has more than 60 million unique users per month of its websites and portals in Europe and the Americas.
OpenX said it had also won Japanese Internet services company Excite as a customer for its newly revamped ad-serving platform, with which it hopes to attract larger publishers by simplifying the way they sell advertising space.
Tim Cadogan, chief executive of OpenX and a former senior manager at Yahoo, said OpenX could now help publishers by bringing together data from separate sources of direct sales, spot markets and exchanges and sales to ad networks.
"Publishers today are basically trying to balance and optimize across multiple revenue streams," he told Reuters by telephone. "We bring it into one coherent package."
Four-year-old OpenX has been steadily making inroads into the online ad market that is dominated by Google, Yahoo, Microsoft and AOL, and now serves more than 350 billion ads per month.
Google bought DoubleClick for $3.1 billion in 2008 after Microsoft bought aQuantive and before leading ad agency WPP bought 24/7, as all the top players scrambled to strengthen their online ad services.
Global Internet advertising revenues are expected to rise 14 percent this year, according to Publicis media buying agency ZenithOptimedia, outpacing 4.6 percent growth in the wider ad market and accounting for 15 percent of all ad sales.
(Editing by Hans Peters)