eBay's growth in the next few years will come mostly from online payment system PayPal, writes Business Insider.

The online auction giant expects PayPal revenues to double to roughly $4-5 billion in sales by 2011. Last year, PayPal reported $2.4 billion in sales, or about 30% of eBay's $8.5 billion of overall sales.

The company also expects Skype to be a $1 billion business in 2011.  Skype reportedly hauled in $551 million in sales last year - 80% growth in three years. It isn't immediately evident whether Skype's growth will be tempered by competitive new rivals, such as Google Voice, which went live today and boasts less expensive international calling features, among others.

Early in 2008, eBay's management dropped hints that Skype — acquired in 2005 for $2.6 billion — was not showing as much value as the company expected, and that they would "test synergies" during the year to meet performance targets, ArsTechnica reported.

eBay's core auction business has slowed considerably. Traffic to the website petered out over the holiday season, and reported a 16% drop in fourth-quarter revenue. This year, business is expected to grow less quickly than the e-commerce market at large.

CEO John Donahoe told the Wall Street Journal that the company would track market growth in 2010 and surpass it in 2011, however.

eBay shares closed up 4.8% yesterday at $11.63.

In June '08, eBay announced two acquisitions while laying off over 1,000 staff worldwide. It paid almost $1 billion for US online payment company Bill Me Later, and around $390 million in cash for the operator of two Danish classifieds sites, dba.dk and bilbasen.dk.

Last year eBay's generation-late technology platform caused analysts to downgrade shares from "neutral" to "overweight."