Celldex Therapeutics (NASDAQ:CLDX), Helmerich & Payne, Inc. (NYSE:HP), and SodaStream International (NASDAQ:SODA) are three top stocks our Motley Fool contributors think you can buy now for significant gains. All three of these companies have compelling catalysts coming up that could spark a rally in shares, so let's learn more about them and find out if they're worth owning in your portfolio. After all, if these stories pan out, they just might double your investment.

A second shot at success

Todd Campbell (Celldex Therapeutics): Let's be honest: No one knows if a stock is going to double or go to zero. But there's enough that could go right at Celldex Therapeutics that give its shares a shot at doubling.

A businessman stands with arms raised as money falls down around him.


Celldex Therapeutics got pummeled last year after its once-promising brain cancer drug, Rintega, failed in clinical trials. Shares haven't made headway since then, but that could be about to change, depending on how trials pan out for another one of its drugs, glembatumumab vedotin (glemba).

Glemba is in trials as a therapy for triple-negative breast cancer, a notoriously tough-to-treat cancer with a poor prognosis and limited treatment options. Glemba binds to a protein expressed by cancer cells and then releases a toxic payload that can kill the cancer cell. It's a bold approach, and if successful, the FDA could grant glemba an early approval. Results from this trial could be reported this year.

Shares could also pop if management reports positive data for glemba in uveal melanoma, or positive data for another one of its drugs, varlilumab, which may improve the cancer-fighting capability of commonly used lung-cancer drugs.

However, this stock is admittedly a long shot. Trials could fail spectacularly, and if so, then this stock could be an investor's death trap (again). Nevertheless, if trial results are good, the payoff could be big. After all, glemba's market opportunity in breast cancer alone could justify Celldex Therapeutics' current $400 million market cap.

Riding the next oil upturn

Reuben Gregg Brewer (Helmerich & Payne): After oil prices started falling in mid-2014, oil and gas drilling services company Helmerich & Payne stock plummeted as much as 45%. The company is in a highly cyclical industry, so that drop makes a lot of sense. In fact, at the end of fiscal 2016, just 25% of the company's U.S. drill rigs were working. That's Helmerich & Payne's bread-and-butter business, accounting for roughly 90% of its fleet.  

But fleet utilization for the U.S. segment was up to 31% by the end of the company's fiscal first quarter. The big change is the oil price rebound that's led to increased drilling. Giant ExxonMobil, for example, recently inked a deal that will double its Permian Basin resources. And just days later, the energy giant announced that its capital spending will increase roughly 14% in 2017. Smaller drillers, meanwhile, have been moving more aggressively than the oil majors.

Helmerich & Payne happens to have one of the most advanced drill fleets in the industry. So it's not a stretch to expect it to get called early and often as drilling activity increases. And if that happens, the company's top and bottom lines will rebound quickly, and so, too, should the stock price. With the shares still off over 40% from the last cyclical peak, Helmerich & Payne could easily double your money as the oil rebound gains steam. And you'll collect a 4% yield while you wait, adding to your returns.     

Bubbly returns

Demitrios Kalogeropoulos (SodaStream): At-home carbonated-beverage specialist SodaStream has tripled over the past 12 months, but I see room for more market-thumping gains ahead. Sure, its annual revenue base isn't likely anytime soon to reach the $563 million peak it set back in 2013. Yet management's branding and operating reboot, which contributed to a sales and profit free fall in 2014 and 2015, has put the company in a far better position to log sustainable growth.

SodaStream recently returned to sales gains as its new sparkling water focus struck a chord with customers. The company sold 22% more starter kits over the holiday quarter, led by a 20% spike in the key U.S. market. Better still, cost cuts and a revamped production infrastructure combined to supercharge earnings growth. In fact, its $44 million of net income last year trounced the prior year's $12 million haul while beating the company's past record from 2012.

SodaStream still converts an unimpressive 7% of sales to net profit, but that figure should climb back into double digits as its machines continue winning market share. The real test -- and profit payoff -- comes in subsequent years, though, when steady carbonation machine use pushes consumables such as carbon dioxide canister refills and water flavorings up to a higher proportion of the business. These products deliver profitable, recurring revenue that could help SodaStream grow into a $2 billion business over time.  

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.