NEW YORK CITY-One of the world's biggest office buyers may be switching to 'seller' by year's end. Private equity behemoth the Blackstone Group LP is planning to dispose of 100 US office properties totaling 50 million square feet, which sources value as high as $22 billion, according to a report in the Wall Street Journal.

The WSJ says impetus behind the sale is to return money to investors in funds that liquidate after seven to 10 years. Blackstone built up its portfolio before the downturn in 2006 and 2007, including its buyout of the Equity Office Properties portfolio for $39 billion, which quickly sold for around $36 billion. The paper said if the company sells its remaining properties in Northern California, Boston, New York and Los Angeles for $20 billion, it can bring in an extra $8 billion more than it originally paid.

Last year, Blackstone reigned king as one of the world’s largest CRE investors across several asset classes. The private equity giant completed a $9-billion acquisition of Centro Properties Group’s US portfolio and purchased debt on trophy properties such as 1140 Ave. of the Americas and the Times Square Building at 229 W. 43rd St. in Midtown. According to SEC filings cited by the paper, real estate contributed $1 billion toward the private equity firm's $1.6 billion in pretax economic income in 2011.