What's better than momentum? Mo' momentum. Let's take a closer look at five of this past week's biggest scorchers.

Company

July 12

Weekly Gain

Organovo Holdings (ONVO -1.19%)

$6.01

55%

Anacor Pharmaceuticals (NASDAQ: ANAC)

$6.75

20%

Breitburn Energy Partners (BBEPQ)

$17.97

18%

Ebix (EBIX -10.89%)

$10.98

14%

Sirius XM Radio (SIRI -4.43%)

$3.72

10%

Source: Barron's.

Let's start with Organovo Holdings, one of this week's biggest winners. All it had to do was hop from the obscure Pink Sheets and onto the New York Stock Exchange to get noticed. It's all about visibility for Organovo, and it couldn't have timed its leap to a more prolific exchange any better.

Organovo provides functional, three-dimensional human tissues for medical research and therapeutic applications. When you apply the investing craze over red-hot 3-D printing and combine it with medical applications, it makes Organovo a compelling story stock.

The downside is that this is a development-stage company. We're talking about just $0.2 million in revenue in its most recent quarter, and half of that amount came in the form of grant revenue. Expect this one to take wild swings in both directions in the coming weeks.

Anacor Pharmaceuticals moved higher after a well-received presentation by CEO David Perry at the JMP Securities Healthcare Conference. Anacor is a biotech upstart toiling away on novel small-molecule therapeutics stemming from its boron chemistry platform.

Anacor isn't making a lot of money -- and the quarterly deficits will continue for a few years -- but biotech investors are willing to be patient if they believe medical breakthroughs will eventually happen.

Breitburn Energy Partners rose in each of the week's five trading days. Things got off to an encouraging start after the high-yielding upstream master limited partnership received an analyst upgrade on Monday. Baird moved the units from "neutral" to "outperform," less than three months after a downgrade. Then again, the price target of $24 at the time of the downgrade addressed valuation concerns that don't necessarily apply now that the stock has fallen to the teens.

Ebix finally bounced back into the double digits. The provider of enterprise software solutions for the insurance industry cratered last month after Goldman Sachs walked away from its plan to help take the company private amid accounting concerns. Ebix appears to have entered oversold territory, and it helped make its own luck by announcing a new partnership earlier in the week that will expand its offerings in Brazil.

Finally, we have Sirius XM pushing through to close out the week at a five-year high. The satellite-radio provider pumped up the volume after announcing that it closed out the second quarter with 715,000 net new subscribers. Despite all of the fears that streaming apps will kill satellite radio, Sirius XM keeps growing. It's now serving more than 25 million subscribers and boosting its subscriber guidance for all of 2013.