Blackstone Group LP is about to finish raising the largest-ever real-estate fund, which at $20 billion will amplify the investment firm’s influence over prices paid for major office towers, shopping centers and hotels around the world.

The $20 billion that Blackstone has raised from U.S. and overseas pension funds, foreign governments and wealthy individuals is more than twice as large as any fund ever raised by a competitor, according to data firm Preqin.

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