Its stock has climbed 43% in the past year and more than 20% in 2017 alone, including a 1.6% rise yesterday to pass Wells Fargo’s $275 billion market capitalization. (Tencent also made the top ten last summer before shares cratered to end the year.)

Putting Tencent’s ranking in context:

Before Tencent (TCEHY), the top ten most valuable public companies were all American, and all had wide global businesses. Apple, Alphabet, Microsoft and Amazon still top the list; Johnson & Johnson, Exxon Mobil, Berkshire Hathaway, and J.P. Morgan fill it out.

Tencent, by contrast, is almost exclusively Chinese. Only a tiny portion of revenues come from abroad, mostly from online game companies that it recently acquired. And the one business driving Tencent shares upward recently is even more exclusively Chinese: Tencent’s mobile payment system.

Tencent’s social network, WeChat, has brought the company the most attention. It’s the biggest social network in China, now with 889 million monthly average users. Tencent’s online games have also driven sales and profits, and Tencent has closed big overseas acquisitions in Supercell and Riot Games.

But analysts see the potential of a massive mobile payment market in China driving investors’ imaginations wild—and pushing Tencent’s shares to new heights.

Tencent’s payment system passed 600 million monthly average users in December. Those users generated 600 million transactions a day, the company said in its March annual earnings report. “We view mobile payment as the most important highlight in [the fourth quarter of 2016],” J.P. Morgan’s Alex Yao wrote at the time.

By active user count, Tencent passed Alibaba’s Alipay and Paypal (PYPL) to become the biggest online payment platform in the world.

Tencent pulled in more than $1.3 billion in revenue from payments last year, J.P. Morgan estimates. It took in 0.3% of the value of transactions for goods.

But that’s likely just the beginning. Online payments are growing by double digit rates in China as restaurants, convenience stores like 7-11, and others add it at the counter. At many stores in Beijing and Shanghai, it’s easier to pay with WeChat pay than a credit card or cash. J.P. Morgan estimates Tencent and Alibaba (BABA) together could pull in nearly $40 billion in revenue from payments in 2020.

Tencent didn’t end up here by accident. Two years ago it was spending hundreds of millions of dollars on venture capital investments in food delivery, group buying, and house cleaning—not to bet on the next big thing, but to add users for its payment system.

Now the number is 600 million users. It’s no accident investors are excited.