Image: Uber.

Earlier this summer, as Uber was raising $1 billion in fresh capital at a valuation north of $50 billion, I was traveling from the West Coat to the Midwest. Five times I used Uber to get where I needed to go; only once did I use Lyft. Rental cars never entered the equation.

Millions around the world use Uber. Hundreds of millions, or even 1 billion could sign on before an IPO, leading Uber to challenge Facebook's (NASDAQ:FB) record for the largest public market debut of all time.

Seem crazy? Goldman Sachs (NYSE:GS) put $450 million into Facebook at a $50 billion valuation in January 2011. Revenue had soared 154% the year prior, and would go on to grow another 88% in the 12 months following the infusion, S&P Capital IQ reports. At a similar valuation, Bloomberg reports that Uber is growing revenue by 300% year over year.

I'm surprised we that we aren't already talking about Uber at $100 billion. Here are four reasons to believe we'll get to that point soon enough:

  1. Expansion has come easy. As tempting as it can be to think of Uber as a transportation company, it's really a software company with one app that's been optimized for service in more than 300 cities in 60 countries. Uber also extends its app through a programming interface (API) that allows other services to plug in as they wish. United Continental (NASDAQ:UAL) and TripAdvisor (NASDAQ:TRIP) are among the many to have taken advantage.
  2. Overseas rivals are banding together to respond. Opposition to Uber has been rising for a while. From taxicab unions to regulators, and even some analysts, there are plenty who want to see Uber fail. And yet the odds seem to be stacked against them. To respond, a group of Uber's overseas rivals are banding together to battle the beast. Didi Kuaidi in China and Lyft in the U.S. made their partnership official on Sept. 15. Both companies are in talks with India's Ola and Singapore's GrabTax, The Wall Street Journal reports.
  3. Optionality is alive and well. Uber is extending its portfolio of services at a brisk pace. From leasing cars to drivers to transporting packages to offering ridesharing via UberPOOL, which is attracting at least 100,000 weekly riders in every active city, there are no shortage of ways for Uber to keep growing its revenue base.
  4. Uber's political clout is growing. After a high-profile fight with the New York City Mayor's office, Uber, in July, convinced regulators to drop a proposed cap on growth under the guise of studying the impact car services have on traffic. An estimated 17,000 users weighed in during the campaign, Re/code reports. Celebrities also piled on via social media. In each case, there's no mistaking Uber's clout, which should serve the company well as it expands into new and highly regulated territories.

Staggering growth demands a staggering price
Whether Uber continues to grow by 300% annually or a fraction of that, what's clear is that investors think this is one of the great growth stories of our time. They've now poured $8.2 billion into the company since its founding six-and-a-half years ago, Crunchbase reports.

Do you think they're right? Would you invest in an Uber IPO? Write to me at Twitter or Google+. I'd love to hear from you, or I may use your comment in a follow-up story.

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.