There's never a shortage of losers in the stock market. 

Let's take a closer look at five of this past week's biggest sinkers.

Company

Aug. 17 Weekly Loss My Watchlist
Lone Pine Resources (NYSE: LPR) $1.33 (40%) Add
Groupon (Nasdaq: GRPN) $4.75 (36%) Add
Idenix Pharmaceuticals (Nasdaq: IDIX) $5.90 (26%) Add
Molycorp (NYSE: MCP) $9.84 (24%) Add
Staples (Nasdaq: SPLS) $11.34 (15%) Add

Source: Barron's.

Lone Pine Resources was a gusher after the Canadian explorer and developer of natural gas and light oil posted disappointing quarterly results. Raymond James downgraded the stock.

Investors used to joke that Groupon is selling at 50% off its IPO, but now the daily-deals leader -- or bleeder -- is trading for more than 75% off its IPO price of $20 late last year. A brutal quarterly report was the negative catalyst this time around.

Idenix slipped after the Food and Drug Administration placed a partial clinical hold on the biotech's once-promising hepatitis C treatment. The agency is now requesting more of the drug's safety data.

Molycorp fell closer to Earth after the rare-earth minerals producer completed a dilutive offering of common stock and convertible debt. Analysts generally panned the company's fundraising efforts.

Finally, we have Staples taking a hole puncher to its investors. The office-supply superstore chain posted lower-than-expected quarterly results. Weakness overseas is holding the retailer back. Citigroup downgraded the stock on the disappointing report.

Ready for a bounce
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