Facebook ad prices more than doubled last quarter

"The News Feed is becoming expensive territory as more users spend time on mobile devices where that’s the only advertising space. (no right-hand rail advertising on the small screen.)
The more than doubling of the cost of ad units was “driven by the shift toward mobile usage where people are shown fewer ads compared to desktop,” David Wehner, Facebook’s chief financial officer, told analysts in a call today following results.
Facebook showed 25 percent fewer ads last quarter, so the boom in revenue comes even as the number of ads decline.
Facebook has more than 1 billion mobile users and 62 percent of ad spending falls under that category—$1.66 billion last quarter."

Source:  AdWeek, 23rd July 2014