Dow Jones Newswires | Discover Financial Services was among the top gainers in a buoyant Standard & Poor’s 500 Thursday, outpacing the broader index as speculation swirled of a possible takeover, though there appeared to be little factual basis behind the reports.

The volume of trading in the credit-card company was higher than average as the stock rose 8% to $13.57 in recent action. Peers Visa Inc., MasterCard Inc. and Capital One Financial Corp. each rose around 5%, all on less than half of typical volume.