Buyout funds sitting on half a trillion dollars committed by investors may need more than a decade to put the money to work if mergers and acquisitions continue at the current pace.

Firms led by Blackstone Group LP and Kohlberg Kravis Roberts & Co. announced $87 billion in deals over the past 12 months, according to data compiled by Bloomberg News.

At that rate, it would take until the middle of 2021 to invest an estimated $503 billion in unspent money, assuming they borrow half the purchase price. Firms usually have three to six years to deploy commitments.

The record amount of capital, most of it raised during a three-year boom that ended with the financial crisis, coupled with fewer and smaller purchases, means firms may have to ask for more time or release investors from capital commitments if they cannot put the money to work.

The funds that may eventually face the toughest time are the industry's largest, raised in 2007 and 2008. TPG has $15.3 billion left of an $18.9 billion fund raised in 2008, according to a person with direct knowledge of the fund. A European fund raised by CVC Capital Partners Ltd. in the same year has $11.3 billion left of $14.2 billion, according to the London researcher Preqin Ltd.

TPG and CVC declined to comment.

Of the $503 billion in unused capital, $86 billion is from funds raised between 2004 and 2006, Preqin data shows. Funds raised in 2007 and 2008 account for $310 billion in so-called dry powder.

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