Silver Lake is in talks to take Workday private in a deal that would rank among the largest software buyouts ever, according to Reuters. News of the negotiations sent Workday's shares up nearly 18% on Thursday, closing at $206.45 and giving the Pleasanton, California company a market value of about $51.1bn. A transaction of that size would almost certainly require Silver Lake to bring in partners.

Last year the firm teamed with Saudi Arabia's Public Investment Fund and Affinity Partners on the roughly $55bn take-private of Electronic Arts. One of the people said additional investors could again help finance a Workday deal.