The ride-hailing giant now has more than 40 million monthly active riders worldwide, co-founder and CEO Travis Kalanick said on Wednesday at Vanity Fair’s New Establishment Summit in San Francisco. In the last month, the company paid out between $1.5 billion and $2 billion to drivers, after taking a cut from fares, he added. And Uber riders spend $50 on average on the service every month.

Uber, which Kalanick co-founded in 2009, now operates in more than 500 cities around the world, and provides a range of services, including rides in black cars, a low-cost ride program, and a meal delivery service, among others.

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One increasingly growing ride option is UberPool, the company’s short-distance carpooling service it debuted two years ago. Today, UberPool rides make up about 20% of all Uber rides globally, Kalanick said on Wednesday.

In March, Uber said that UberPool rides accounted for more than half of all rides in some cities, and that in China, it was running 20 million UberPool trips per month. (In August, Uber announced it was merging its Chinese business with local rival Didi Chuxing, effectively exiting the company.)

Kalanick also reiterated the “existential” importance of self-driving cars to Uber. Since making public last year its ambitions to build self-driving car technology, Uber has forged several partnerships, including with Volvo, and it recently acquired Otto, a startup building self-driving trucks.

Kalanick also clarified that while Uber is working on autonomous cars, the company doesn’t intend to shift toward owning all their cars one day, which are currently being used to ferry passengers and make deliveries. Ownership of these fleets could take many forms, he added.