BC Partners and Silver Lake are set to buy healthcare services firm Multiplan for $3.1 billion in the largest secondary buyout of the year, a source familiar with the situation said on Friday.

BC Partners and Silver Lake are buying the company, which provides systems to reduce the cost of healthcare claims, from rival buyout firms Carlyle and Welsh, Carson, Anderson & Stowe.

The deal is another example of private equity firms buying companies from each other as they look to deploy hundreds of billions of dollars of unspent funds.

BC and Silver Lake together own a majority of satellite services group Intelsat and previously partnered in Unitymedia , the German cable television provider.

The deal marks BC's fifteenth acquisition out of its current 5.8 billion euro ($7.36 billion) fund, raised in 2005 before the peak of the leveraged buyout (LBO) boom.

It has spent about 85 percent of the capital and aims to start a new fundraising drive later this year.

(Editing by Erica Billingham)

($1=.7885 Euro)