Walmart, which generated $611 billion in sales in 2022, has been sitting pretty as the biggest company on the planet by revenue for 10 years straight. But it needs to watch its back. 

Thanks to the Ukraine war’s impact on oil and gas prices and Saudi Arabia’s ability to cheaply pump oil from its immense reserves, Saudi Aramco had a banner year. It narrowly missed the top slot with $604 billion in revenue, up 51% from the year prior. Even more impressively, Saudi Aramco earned $159 billion in net income, racking up the most profitable year ever for a Global 500 company. If the energy industry has another surge like that in 2023, Walmart could get knocked off its perch. 

But here’s the thing: Like the leaders of the world’s other giant crude oil producers, the folks at Saudi Aramco are also looking over their shoulders. They know that a global green transition will eventually end their dominance, unless they get serious about the alternative-fuel business. That’s one reason why the Saudi government, which controls Aramco, is plowing its profits into green-tech R&D and a host of other industries, as Vivienne Walt explains in her story in this issue.

A little further down the list, a different earthquake is underway. Alphabet, which ranks No. 17 on this year’s Global 500, is facing a classic innovator’s dilemma thanks to generative A.I. Alphabet’s Google has thrown more money and expertise at A.I. than just about any other tech giant. But now, that same revolutionary technology is threatening the search business that has fueled Google’s profit-making machine since the 2000s. 

The No. 1 Threatener is Microsoft (No. 30 on the G500), thanks to its partnership with ChatGPT creator OpenAI. Microsoft CEO Satya Nadella has needled Alphabet’s Sundar Pichai and his engineers, saying, “I want people to know that we made them dance.” 

Pichai’s predicament is tricky. Google needs to fight Microsoft and other A.I. rivals with its own, better product—and as Jeremy Kahn reports in this issue, Pichai and his team are doing just that. Whoever builds the best mousetrap in generative A.I., whether it’s Google, or Microsoft, or Meta (No. 81), or some as-yet-unknown startup, could transform how the world searches for information. But Google is earning $160 billion a year from search and advertising based on the status quo. If the way people use the internet is greatly changed by technologies like chatbots or personal assistants, there is no guarantee Alphabet can protect that cash cow—and it has no obvious revenue substitute at that scale.

To see the authoritative ranking of the current corporate world order, see our full list here. To find out what the new order will look like, keep reading here. We can’t wait to report how it all unfolds for you.

Alyson Shontell
Editor-in-Chief, Fortune
@ajs

This article appears in the August/September 2023 issue of Fortune with the headline, “Tech-tonic shifts.”