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

May 31

Weekly Loss

Frontline (NYSE:FRO)

$1.86

19%

Velti (NASDAQOTH:VELTF)

$1.76

13%

Yingli Green Energy (NYSE:YGE)

$2.85

11%

Portugal Telecom (NYSE:PTGCY)

$4.21

10%

Exelon (NYSE:EXC)

$31.34

10%

Source: Barron's.

Let's start with Frontline. The oil tanker company posted a narrower loss than Wall Street was expecting, but a gloomy outlook sank the shares. Frontline has a big debt repayment milestone in two years, and it fears that an oversupply of tankers is holding back the recovery it needs if it doesn't want to run out of money.

Velti continues to slide after posting disappointing quarterly results earlier in the month. Shareholders of the Irish mobile marketing services provider have been slammed hard in recent months. The stock has shed 83% of its value since peaking last summer.

Yingli Green Energy was no solar-energy star after posting fresh quarterly financials. Yingli's revenue exceeded expectations, but this was the fourth consecutive quarter in which it posted a much wider loss than the deficit analysts were forecasting.

Another analyst has soured on Portugal Telecom. Berenberg Bank is downgrading the Portuguese telco giant from "buy" to "hold." Goldman Sachs had talked down the shares four weeks earlier.

Finally we have Exelon tumbling after an analyst downgraded the utility bellwether. Deutsche Bank's Jonathan Arnold lowered his rating on Exelon from "buy" to "hold" on fears that the company will face pricing pressure come 2016.

Ready for a bounce
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Longtime Fool contributor Rick Munarriz has no position in any stocks mentioned. The Motley Fool recommends Exelon and Goldman Sachs. Try any of our Foolish newsletter services free for 30 days. We Fools don't 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.