U.S. exchange-traded fund assets increased by $292.7 billion or 28% in 2012, in part driven by positive cash flows of $182.6 billion, marking a new all-time high for the industry on the eve of its 20th anniversary, according to data fromState Street Global Advisors.

In December, U.S. ETF inflows topped $28 billion, as investors poured $15.6 billion of new inflows into large cap ETFs and $8.4 billion into emerging market ETFs.

The top three managers in the U.S. marketplace were once againBlackRock,Vanguardand SSgA, accounting for some 84% of the US-listed ETF market.