Small-cap stocks, which are usually defined as companies sporting a $300 million to $2 billion market cap, can be risky because they often lack time-tested business models. However, they also offer superior growth potential, and when you find a winner, the rewards can be enormous over the long term. 

So we asked three Motley Fool contributors to name a small-cap stock in which they see a lot of potential right now. They think that at the top of your buy list should be drug stocks Viking Therapeutics (VKTX 1.60%) and Acceleron Pharma (XLRN), along with mining company SSR Mining (SSRM -0.68%)

An ascending pile of prescription tablets on a messy pile of hundred dollar bills.

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A winner that should keep on winning

Keith Speights (Viking Therapeutics): In July, I picked Viking as one of the top biotech stocks to buy for the second half of 2018 despite the fact that it had already chalked up a 130% year-to-date gain at the time. Since making that call, Viking has nearly doubled, but I think it can go a lot higher.

The big recent catalyst for Viking was some really positive results from a mid-stage clinical study evaluating VK2809 in treating nonalcoholic fatty liver disease (NAFLD) and elevated LDL cholesterol. Viking's experimental drug particularly showed promise in treating one type of NAFLD -- nonalcoholic steatohepatitis (NASH). 

That's important because NASH is one of the hottest areas of development in the biopharmaceutical industry right now. Some industry observers predict that NASH could become a $35 billion market within a few years. Viking's success with VK2809 could make it a top acquisition candidate for bigger companies looking to bolster their chances of winning a nice chunk of that lucrative market.

If VK2809 was the only candidate in Viking's pipeline, I'd still like the stock. However, Viking has several other experimental drugs in development. The prospects for VK2511, which helps promote muscle and bone strength after hip fracture surgery, look especially promising. With two possible blockbuster drugs in its pipeline, I think Viking is a winner that should keep on winning.

A biotech lab researcher using multiple pipettes to with test tubes.

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A blockbuster drug with a buyout kicker?

Todd Campbell (Acceleron Pharma): Positive trial results for Acceleron Pharma's beta thalassemia and myelodysplastic syndromes (MDS) drug luspatercept clear the way for regulatory filings and potential OKs in the U.S. and European Union, but that's not the only reason why I'm a fan of this $2.4 billion market-cap company. There's also a chance that collaboration partner Celgene (CELG) will swoop in and acquire it.

Celgene is partnered on luspatercept, and in presentations to investors in the past, its management has said it believes luspatercept could be a foundational product with annual sales potential of $2 billion. As it stands today, Celgene and Acceleron will split profit on luspatercept in the U.S. and Celgene will pay Acceleron royalties on sales in the low- to mid-20% range elsewhere.

There's no telling what Celgene will do, but an argument could be made that it will move to acquire Acceleron outright to avoid having to share profits and make those payments. Celgene already owns 12.3% of Acceleron Pharma, so there's clearly some interest.  

However, Acceleron Pharma could do fine even if Celgene decides against an acquisition. It could begin receiving meaningful revenue from luspatercept as early as 2019, and it's sitting on $332 million in cash and equivalents, which is enough to get it to 2021, according to management.

Overall, Acceleron's trial success has de-risked it relative to some other clinical-stage biotech stocks, and luspatercept's potential is big enough for me to think picking it up now is smart.  

Two gold bars lying next to each other.

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This small cap is about to regain its luster

Sean Williams (SSR Mining): You might not think of the gold and silver mining industry when it comes to the top small-cap stocks to buy, especially with gold near a one-year low, but SSR Mining looks to be a truly exceptional value for patient investors.

SSR Mining, like most metal stocks, tends to ebb and flow with the rising tide of metal prices. The company has also been under pressure with the end-of-life of its San Miguel open-pit silver mine in Argentina. But the good news is things are changing in a big way.

On the gold side of the equation, SSR Mining acquired Claude Resources and its prized Seabee mine in 2016. Since the acquisition, SSR Mining has steadily increased production to record levels while maintaining low all-in sustaining costs that've ranged from $775 to $896 an ounce over the trailing year.

Meanwhile, the company's flagship gold mine in Nevada, Marigold, is slated to grow its annual production by 30% to about 265,000 ounces by 2021 or 2022. This should lead to at least another decade of mining activity at Marigold and approximately 15 years of production.

The other exciting development here is that SSR Mining and Golden Arrow, which entered a 75%-25% joint venture, are set for sustained ore delivery at the Chinchillas Project during the fourth quarter. Chinchillas, which is on SSR's Pirquitas property, will add depth by providing silver production that's been missing in recent quarters.

Not only is SSR Mining expected to see a significant uptick in cash flow in the quarters and years to come, but the company is also financially set with regard to its balance sheet. While many of its peers are nose-deep in debt, SSR Mining has a net cash position of more than $260 million, or roughly a quarter of its existing market cap. It's capable of adding in the neighborhood of $20 million in net cash per quarter, if not more, going forward. 

Valued at less than five times expected cash flow per share by the time 2021 rolls around, SSR Mining looks to be one heck of a value, regardless of how metal prices vacillate in the near term.