Private equity giant Blackstone Group LP (NYSE: BX) is preparing to sell its office portfolio over the next 18 months, hoping to capitalize on the commercial property rebound, the Wall Street Journal reported.

The holdings, which will be turned into packages of properties that are in specific regions, have been valued at as much as $22 billion, according to the Journal. New York-based Blackstone became one of the largest office landlords in the country following its 2007 leveraged buyout of Sam Zell's Equity Office Properties Trust for $39 billion. It almost immediately sold $30 billion in assets, including seven New York towers to developer Harry Macklowe. Many of the buyers defaulted on their new purchases after the credit markets froze in 2008. Blackstone retained properties in California and Boston, and it currently owns around 70 million square feet of space, according to its website.

Shares of Blackstone fell six cents to $12.77 in midday trading.