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

April 26

Weekly Loss

Dyax (NASDAQ: DYAX)

$2.69

37%

Whiting USA Trust I (NYSE: WHX)

$6.74

16%

Mellanox Technologies (MLNX)

$52.08

13%

Safeway (NYSE: SWY)

$23.31

12%

Key Energy Services (KEG)

$5.90

11%

Source: Barron's.

Let's start with Dyax. The small drugmaker shed more than a third of its value after posting disappointing quarterly results. Dyax's revenue of $12 million fell well short of the $16 million Wall Street was expecting, and it didn't help that its deficit was twice as large as projected. However, this is ultimately a problematic snapshot for how its flagship drug, Kalbitor, is faring in the market.

Whiting USA Trust I slipped after a Seeking Alpha article suggested that the oil and gas royalty trust could lose half of its value. The article pegged a fair value of $3.50 on the trust units. Whiting issued a press release the next day, pointing out that the New York Stock Exchange contacted the trust given the unusual market activity, but Whiting's policy is to not comment on the activity.

Mellanox Technologies slipped after Needham & Co. downgraded it following results that actually beat Wall Street estimates. Needham, in marking down the shares from "buy" to "hold," is concerned about Mellanox's lumpy business model and the lack of clarity. Mizuho Securities also downgraded Mellanox.

Safeway investors hit the register after the supermarket chain posted disappointing quarterly results. There wasn't much of a bottom-line miss, and comps were at least positive, but the stock hit a four-year high ahead of the results. Expectations ran too high, and the grocer still trades nearly 30% higher in 2013.

Finally we have Key Energy Services moving lower. The country's largest onshore, rig-based well servicing contractor fell short of Wall Street's profit targets in its latest quarter. Key Energy had beaten analysts' bottom-line estimates with ease in previous quarters, but it proved mortal this time, as demand weakened despite record oil production.

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