REUTERS/Jim Urquhart CEO of AOL Tim Armstrong attends the Allen & Co Media Conference in Sun Valley, Idaho July 12, 2012. 
As everyone in the advertising world gathers in the south of France for the annual Cannes festival, Google and Facebook are top of mind.
More specifically, everyone's talking about how they're afraid of the two online giants' advertising market dominance, AOL CEO Tim Armstrong tells The Wall Street Journal's Jack Marshall.
"It comes up with publishers, with advertising agencies, with marketers," he said. "There's a fear of a duopoly overall."
Before going to AOL, Armstrong ran sales at Google for nearly a decade.
Right now, Google and Facebook control 43% of global ad revenue, according to data from eMarketer (in an eMarketer chart of US ad revenue on the right, AOL is represented by Millennial Media).
Both companies are often described as "walled gardens" because they restrict or make it difficult for marketers to use their own data or third-party measurement tools.
As Kathy Leake, CEO of ad targeting company Qualia recently put it in an op-ed:
"The big guys get bigger, gobbling up the data, while the marketers come away with nothing."
Armstrong said that Verizon-owned AOL is trying to take the opposite approach.
"The larger companies have been getting more difficult with data overall," he said, "So there's an opportunity for us to differentiate by offering a more open approach that allows us to share our data in a protected way with our partners and customers."
