Nearly four out of five consumers using an established login on retailer sites served by Gigya Inc. enter their Facebook credentials, according to a new report from the social media optimization firm. The vendor lets consumers sign into e-retailer sites using their already established logins with such sites as Twitter, Facebook and Google Inc.’s social network Google+.

In the second quarter of this year, 79% of consumers logging into Gigya’s retail clients’ sites did so through Facebook, it says. Another 12% used their Google+ log-in, 4% Twitter, 3% Yahoo, 1% LinkedIn; about 1% used logins from other social media sites. The vendor offered no comparative data from previous quarters.

The vendor, which counts Wal-Mart Stores Inc., Microsoft Corp. and Victoria’s Secret among its more than 200 retail clients, says that Facebook’s dominance of social logins is more pronounced on retail sites than on other sites, such as media sites. For example, 44% of consumers logging into Gigya’s media and publisher clients’ sites did so through via Facebook, while 28% used Google+, 4% Twitter, 21% Yahoo, 1% LinkedIn and 2% other sites.

However, Google+ will likely find ways to gain market share among retail sites, says Patrick Salyer, Gigya CEO. “Google+ will gain a higher percentage of logins as Google Wallet gains traction in the market,” he says. “Consumers’ Google+ identity will be closely tied to Google Wallet and, as that happens, more consumers will choose to log in and ultimately complete their purchases with a unified Google identity.” Google Wallet allows consumers to store their credit and debit card numbers and billing information in one place so they can check out in two-steps from any web-enabled device. When a shopper signs into a site using his Google+ account, a consumer can click a button to access his Google Wallet account.

Amazon and others that are just entering the space will also likely eat into Facebook’s market share, he adds.