53% of Facebook's advertising revenue comes from mobile

"Revenue from advertising was $2.34 billion, a 76% increase from the same quarter last year.
Mobile advertising revenue represented approximately 53% of advertising revenue for the fourth quarter of 2013, up
from approximately 23% of advertising revenue in the fourth quarter of 2012.
Payments and other fees revenue was $241 million for the fourth quarter of 2013."
Source:  Q4 2013 Earnings release from Facebook, 29th January 2013
Full details of earnings here