Last year Ebay's marketplace accounted for 30% of Paypal's revenue. Ebay mentioned that this number is declining and is forecast to hit 15% in the future. So significant but declining.
"That’s no surprise since about 30 percent of PayPal’s business is still on eBay, although that is down from 50 percent only a few years ago. Donahoe said eBay projected it would get to 15 percent quickly."
http://recode.net/2014/09/30/ebay-to-spin-off-paypal-with-ne...
"That’s no surprise since about 30 percent of PayPal’s business is still on eBay, although that is down from 50 percent only a few years ago. Donahoe said eBay projected it would get to 15 percent quickly." http://recode.net/2014/09/30/ebay-to-spin-off-paypal-with-ne...