NEW YORK ( TheStreet Ratings) -- TheStreet Ratings' stock model upgraded ArcelorMittal SA ( MT) to 'Buy' from 'Hold'. Net income at this $51.8 billion market cap bank grew by 67% to a profit of $1.1 billion compared to in the prior first quarter.

TheStreet Ratings released rating changes on 18 U.S. common stocks for May 13, 2011. In total, nine stocks were upgraded and nine stocks were downgraded by our stock model.

In the first quarter, ArcelorMittal reported $22.2 billion in revenue, an increase of 27.3% compared to the year earlier quarter. Learn more about ArcelorMittal: Company Profile, Income Statement, Balance Sheet, Stock Ratios, Analyst Ratings.

$1.0 billion market cap, insurance company, Tower Group Inc ( TWGP) was upgraded by our stock model to 'Buy' from 'Hold'. In first quarter results, Tower Group reported net profit of $25.7 million, up 47.0% from the year earlier quarter. Over the same time period, revenue gained 41.9% to $430.5 million. Learn more about Tower Group: Company Profile, Income Statement, Balance Sheet, Stock Ratios, Analyst Ratings.

-- Reported by Kevin Baker in Jupiter, FL.

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Kevin Baker became the senior financial analyst for TheStreet Ratings upon the August 2006 acquisition of Weiss Ratings by, covering equity and mutual fund ratings. He joined the Weiss Group in 1997 as a banking and brokerage analyst. In 1999, he created the Weiss Group's first ratings to gauge the level of risk in U.S. equities. Baker received a B.S. degree in management from Rensselaer Polytechnic Institute and an M.B.A. with a finance specialization from Nova Southeastern University.

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