What's better than momentum? Mo' momentum.

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

Company

May 18 Weekly Gain My Watchlist
Groupon (Nasdaq: GRPN) $11.58 17% Add
Nationstar Mortgage (NYSE: NSM) $17.02 15% Add
OPNET Technologies (Nasdaq: OPNT) $26.02 14% Add
XenoPort (Nasdaq: XNPT) $5.83 12% Add
KiOR (Nasdaq: KIOR) $9.95 11% Add

Source: Barron's.

Groupon bucked the trend of last week's brutal market, climbing 17% higher after posting strong quarterly results. The daily-deals specialist began the week at less than half of its recent IPO price, so investors probably got the most out of this "50% off" deal.

Nationstar served up strong growth in its latest quarter. The servicer of residential mortgage loans saw its net income soar 237% on a 35% uptick in revenue.

OPNET Technologies moved higher after also delivering encouraging financials. The provider of network performance management solutions may have frightened investors last month when it warned that purchasing delays would sting quarterly results, but it came up at the very top of its revised guidance. It also had good news on the completion of the quarter's purchasing delays.

XenoPort didn't have any material news to report on the week, but the company's been a big winner during this ugly month for the market. Shares of the biotech targeting neurological disorders have gained nearly 28% in May.

Finally we have KiOR posting double-digit gains last week after revealing that its first commercial facility is ahead of schedule.

More winners for you
It was a great week for these five stocks. If you want to get an early read on some of tomorrow's major gainers, there's a special report on three hidden winners in a booming industry. The report is free -- like this article -- but it won't be around forever, so check it out now.