Money may not grow on trees, but a little water — okay, liquidity — never hurts. With the world a wash in funds that investors are eager to put to work, few companies have benefited more or found it easier to pros-per than investment management firms. And no wonder: Assets under management at America’s 300 biggest money managers, the Institutional Investor 300, grew a smart 16.9 percent in 2006, to reach $31.1trillion. That was nearly twice the rate of growth in 2005 and marks an increase of two thirds from five years ago, when the II300 managed $18.6 trillion. The minimum required to make this elite group continued to climb sharply: The smallest firm on our list, NewYork hedge fund manager Eton Park, reported assets of $6.3 billion, an entry hurdle that is $1.1 billion higher than in the previous year.

Leading the way for a third straight year is Barclays Global Investors, powered by strong investor demand for the firm’s enhanced index products, its exchange-traded funds and, more broadly, its alternative-asset offerings. At year-end San Francisco–based BGI managed $1.8 trillion, up 19.9 percent from 2005. “Our business was strong in 2006, with net new asset growth of approximately $68billion,” says CEO Blake Grossman.

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