VentureBeat reported PayPal's processing of mobile payments hit nearly $4 billion last year. That's slightly above the $3.5 billion the company had projected back in October. VentureBeat spoke with David Marcus, PayPal's VP of mobile.

While still only a small fraction of the approximately $100 billion PayPal processes annually, the $4 billion in mobile payment volume represents a more than fivefold increase over the $750 million in mobile payment volume in 2010, itself a fivefold increase over the volume in 2009.

According to Marcus the growth was due to an overall increase in mobile commerce  and "more useful mobile payments apps."

Marcus also mentioned that PayPal is one of the most popular methods for topping off a Starbucks mobile payment account. 

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