Costco (COST), Exxon Mobil (XOM) and Morgan Stanley (MS) were among some of the widely held stocks downgraded by Louis Navellier in his latest fundamental stock analysis on March 29, 2010.

Costco (COST) missed expectations in its March earnings report despite strong international sales. Costco didn’t offer an outlook but said its fiscal second-quarter results were in line with internal projections. Costco was downgraded from “Buy” to “Sell.”

Exxon Mobil (XOM) is making a $28.5 billion bet on natural gas even as most Wall Street experts are betting on prices falling, according to a Bloomberg news report. Exxon was downgraded from a “Sell” to a “Strong Sell.”

Morgan Stanley (MS) recently has been chosen to underwrite and advise the government as the United States looks to sell its nearly 30% stake in Citigroup (C). Morgan Stanley was downgraded from a “Sell” to a “Strong Sell.”

A complete look at this week’s downgrades among widely held stocks is below. Also please check out this week’s stock upgrades.

About Portfolio Grader: Every Sunday, renowned growth stock adviser Louis Navellier runs a fundamental analysis on the top 5,000 Wall Street companies. Armed with this research, Navellier offers a rating for each company reflected as  a simple letter grade, with A being “strong buy” and F being “strong sell.” Portfolio Grader’s stock data is free and open to the public, and can be accessed online here.