Insurance group Admiral has been approached by several parties about price comparison site Confused.com.
"The Board is reviewing its options in relation to Confused which include retention of the business or a partial or full disposal," Admiral said.
Analysts estimate that the business could fetch between £600m and £700m.
Confused.com started as a car insurance comparison site and now covers home insurance, loans, credit cards and utility bills.
Admiral was set up in 1993 and employs more than 2,000 people at offices in Cardiff and Swansea.
Last year it reported profits before tax of £147.3m, of which £23m came from Confused.com.
Reports have suggested that one of the potential bidders is InterActiveCorporation, which owns Ticketmaster and Ask.com.
Its chairman is US businessman Barry Diller, who is also chairman of the internet travel agent Expedia.com.
Deals involving price comparison websites have been in the news recently, with Moneysupermarket.com rumoured to be considering a £1bn stock market listing.
Simplyswitch was bought by Daily Mail and General Trust last August while Uswitch was bought by the US media firm EW Scripps in March 2006.