U.S. exchnage-traded funds assets totaled $1.12 trillion as of May 31 – up 7% year-to-date, according to the ETF Snapshot May 2012 released by State Street Global Advisors.

In May, investors added $5.3 billion more to ETFs than they withdrew - despite disappointing equity performance (the S&P 500 Index decreased 6 percent while the MSCI EAFE Index fell 11.5 percent during the month).

Fixed income ETFs posted a category-leading $7.9 billion of inflows in May, increasing year-to-date inflows to $28.4 billion.

The international – emerging markets category had the most significant outflows with $3.5 billion leaving the category.

The top three managers in the United States ETF marketplace were: BlackRock, with 276 ETFs handling nearly $469 billion in assets and accounting for 41.7% of the market-share; State Street, with 112 ETFs handling nearly $269 billion in assets and accounting for 23.9% of the market-share, and finally Vanguard with 64 ETFs handling nearly $201 billion and accounting for 17.9% of the market-share.

Tommy Fernandez writes for Money Management Executive.