The $620m price tag for Shopping.com, a Nasdaq-listed company, represents a price of $21 a share. The company's shares had been trading at $17.44 when the market closed on Wednesday, before the deal was revealed.
The deal will see eBay listings added to the product selection already available on Shopping.com, and Epinions, the consumer-generated reviews on Shopping.com, will be used to complement eBay's community feedback ratings.
Bill Cobb, president of eBay in North America, said: "Shopping.com's comparison technology simplifies the online shopping experience and the Epinions' community of reviewers is a great match with our own."
The deal is eBay's biggest acquisiton and it follows its purchase of Indian shopping website Baazee.com, the largest online marketplace in India, in a deal valued at $50m last June.
EBay said it expected the deal to be completed by the third quarter of the year. The company's other acquisitions include PayPal, the online payment company it bought in 2002, and in December last year it bought Rent.com, the US flat-finding website.
Shopping.com's Epinion service features almost 2m detailed reviews of products and services from a network of 400,000 users.
"EBay will provide our shoppers greater convenience and comprehensiveness and will help our merchants increase sales," Lorrie Norrington, president and CEO of Shopping.com, said.
"This partnership will allow Shopping.com to accelerate our vision to dramatically improve the way people shop and sell online."
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