The WSJ reports that the company has been "quietly" trying to get out of the partnership since Marissa Mayer took over as CEO in mid-2012.
Yahoo and Bing are in a 10-year partnership that sees Bing power Yahoo search in exchange for a 12 per cent cut of the revenue brought in by search advertising and the like.
But Yahoo isn't getting enough out of the deal - the source told WSJ that its income per search is lower now than it was when Yahoo ran its own search engine.
Even the filing earlier this week of an agreement to extend the guaranteed revenue that Bing would provide has not quelled Yahoo's disquiet.
Mayer joined Yahoo from Google, and word is that her old employers have offered Yahoo a more lucrative deal - although it's thought that any such deal would face fierce anti-competitive scrutiny.
Neither Yahoo nor Microsoft has anything of note to say other than that all is merry and bright between them, and it's thought that if Yahoo does find a way out, it won't be able to extricate itself from Bing until 2015 at the earliest.
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Former UK News Editor for TechRadar, it was a perpetual challenge among the TechRadar staff to send Kate (Twitter, Google+) a link to something interesting on the internet that she hasn't already seen. As TechRadar's News Editor (UK), she was constantly on the hunt for top news and intriguing stories to feed your gadget lust. Kate now enjoys life as a renowned music critic – her words can be found in the i Paper, Guardian, GQ, Metro, Evening Standard and Time Out, and she's also the author of 'Amy Winehouse', a biography of the soul star.