The five heirs to Wal-Mart Stores Inc. fate became$ 5 billion richer Tuesday after the world’s largest retailer said it expects U.S. e-commerce sales to surge 40 percent in the next fiscal year. The forecast added 4.5 percent to Wal-Mart shares and pushed the combined net worth of Alice, Jim, Rob, Lukas and Christy Waltonto $140 billion, according to the Bloomberg Billionaires Index.

That widened the gap between the Waltons and Amazon.com Inc.’s Jeff Bezos, whose fortune has surged 74 percent in the past two years. Bezos overtook Bill Gates as the world’s richest person for just a few hours in late July, when his net worth peaked at $92.3 billion.

Wal-Mart’s upbeat guidance, issued ahead of its annual shareholder session, triggered the most difficult rally in the company’s shares in more than a year, lending credence to the view that its bet on e-commerce is beginning to pay off. Wal-Mart also said it plans to add 1,000 online-grocery locations. Amazon purchased Whole Foods Market Inc. the beginning of this year for $13.7 billion.

Bezos’s fortune has risen from about $17 billion when the Bloomberg index debuted in March 2012, a gain of 371 percent. The Waltons have added 48 percent.