Over the past decade, shares of the SPDR S&P 500 ETF (NYSEMKT:SPY) have jumped over 300%. This has been one of the best runs for the history of the S&P, but these two stocks could outperform this stellar performance.

Both MercadoLibre (NASDAQ:MELI) and Upstart (NASDAQ:UPST) have been amazing companies to own since they came public, but the growth runway for both companies is still huge. Each company could produce 5-fold returns if you put $100,000 in each company today and wait a decade. Here's why. 

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MercadoLibre: The Latin American "everything" company

MercadoLibre grew to become $65 billion in size because of its successful e-commerce operations, but the company has massively expanded its optionality and its revenue streams. Now the company makes money in its dominance in logistics and payment markets across 16 countries in Latin America. 

The company is seeing broad adoption from its newer services, and some of its new services are even growing faster than its primary segment -- its e-commerce business. Its logistics arm -- Mercado Envios -- shipped over 247 million items in Q3, and 86% of the company's e-commerce shipments were shipped with Envios. 37% of all fulfillment in MercadoLibre's areas of operation go through Envios, which flexes its broad adoption across the region.

Mercado Pago -- its payments platform -- has 31.6 million unique active users and nearly $21 billion in total payment volume. This grew 44% from Q3 2020, and its payment transactions almost reached 700 million, growing 67% year over year.

All of this is in addition to the company's core business: MercadoLibre. Its e-commerce segment brought in over $1.2 billion in revenue after the company grew its gross merchandise volume 24% year over year to $7.3 billion. The company also sold 260 million items during the quarter, which grew 26% from Q3 2020. 

MercadoLibre's market opportunity is large, and that is only amplified with its new business segments. The company has over 79 million users on its platform, but there are over 646 million citizens in its reach. Latin America is growing at one of the fastest rates in the world, so MercadoLibre's penetration is in its early days. Even this 79 million count doesn't factor in the fact that consumers might use its e-commerce platform but not Mercado Pago, meaning MercadoLibre has room to grow its relationships with its existing customers and its customer base. 

The company does face competition in some parts of its business, like its e-commerce segment where it faces Sea Limited in several markets. However, MercadoLibre is not fully reliant on its e-commerce brand and Sea Limited is only getting started in Latin American markets outside of Brazil, so it is not a huge threat to the whole business. The company's fast-growing business segments show that the company has the capabilities to succeed but has yet to fully grow. This allows for investors like you and me to get in today and reap the mass benefits of the company's potential success over the next decade. 

Upstart: Rapid adoption and success

While Upstart is not the established business that MercadoLibre is, the company still has amazing potential to 5 times from today's prices. For decades, we have used the FICO score -- a metric created by Fair Isaac Corp. -- to determine creditworthiness despite its flaws. For example, consumers who do not use credit or have made one minor error in their past could have their credit score wrecked and would be denied good credit. Upstart realizes that the FICO score is not a fully accurate representation of creditworthiness, so the company is using artificial intelligence (AI) to create a new way to do this. 

The company's determination does come from factors like employment, income-to-debt ratio, and other traditional metrics, but these are in addition to thousands of other non-traditional factors like education or loan application interaction. This innovative way of rethinking credit has resulted in rapid adoption from many banks and credit unions. The company has tripled its customer count from 10 one year ago to 31 in Q3. 

Despite being a $16 billion company, it is growing revenue at staggering rates of 250% year over year, reaching $228 million in Q3. What is even better is that the company is profitable. Upstart earned a net income of $29 million, which grew 200% year over year. 

Upstart is seeing success in disrupting a major financial cornerstone, so it is understandable that the company will be valued highly. Upstart currently trades at 28 times sales and 238 times earnings. While these are high, Upstart shares have fallen nearly 50% off their all-time high, so this is a nice discount to the 60 times sales and 600 times earnings shares were trading at in late September. 

The FICO score is inaccurate and inefficient for many Americans, and Upstart is trying to make getting a loan easier for those people. The company has begun to see widespread success, but with an addressable market of over $5 trillion, the company is very early on its journey. If Upstart can continue refining its AI system to maintain its accuracy while obtaining more customers across the country, the company could continue to explode over the next decade, providing stock returns of 400% or more. 

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.