While Fools should generally take the opinion of Wall Street with a grain of salt, it's not a bad idea to take a look at particularly stock-shaking analyst upgrades and downgrades -- just in case their reasoning behind the call makes sense.

What: Shares of Transocean (NYSE:RIG) slipped 1% this morning after Goldman Sachs downgraded the drilling giant from "neutral" to "sell".

So what: Along with the downgrade, analyst Waqar Syed lowered his price target to $50 (from $53), pretty much exactly where the stock closed on Friday. While momentum traders might be attracted to Transocean's recent pop -- fueled by its addition to the S&P 500 Index -- Syed believes that the rally is particularly unsustainable due to the unfavorable industry trends working against the company.

Now what: Goldman sees significant headwinds in Transocean's near and long-term future. "The key catalyst for offshore drillers is increases in dayrates, and rates have flattened for UDW (ultra-deepwater) rigs while early signs of utilization/dayrate weakness in the deepwater market are emerging," noted Goldman. "RIG faces structural challenges as its floater fleet is aging and it needs to make sizable investments to high grade its fleet. It has taken some recent steps in that regard, but needs to do more." When you couple those risks with the stock's seemingly steep P/E of 25 -- a clear premium to peers -- I'd have to agree that Transocean's recent surge is a bit overdone. 

Fool contributor Brian Pacampara has no position in any stocks mentioned. The Motley Fool owns shares of Transocean. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.