eBay Inc Chief Executive John Donahoe increased a key forecast for the company's PayPal payments business during an Internet industry conference on Monday.

Donahoe said total payment volume, or TPV, transmitted by mobile devices through PayPal's system will be more than $3.5 billion in 2011, during a discussion on stage at the Web 2.0 Summit in San Francisco.

The CEO's previous forecast was for $3 billion in mobile TPV at PayPal this year.

EBay is making a big push into mobile commerce, through smartphone apps like Red Laser, which lets shoppers scan bar codes to check prices online and at other retailers nearby.

PayPal is trying to transform itself from an online payments business into a mobile payments service that works in the offline world too.

Investors are watching for signs of progress in these areas because they increase the size of eBay's potential market hugely.

Last week, Donahoe said eBay's main Marketplaces business will process almost $5 billion of gross merchandise volume via mobile devices this year. That was up from a previous estimate of roughly $4 billion.

(Reporting by Alistair Barr, editing by Bernard Orr)