Wal-Mart is more than three times larger than its nearest competitor, a study of the world's largest and fastest growing retailers has found.
The firm had sales of $287bn (£160bn) in 2004-5, more than its three closest rivals put together, the Deloitte 2006 Global Retailing Powers study showed.
Tesco rose to fifth in its table, behind Carrefour, Home Depot and Metro.
Success in China, India and Russia may help determine which firms challenge Wal-Mart in the future, Deloitte said.
Chasing the leader
Tesco, France's Carrefour and Germany's Metro are all aggressively expanding in China, while Wal-Mart plans to hire 150,000 staff there over the next five years.
"The likes of Tesco, Carrefour and Metro would see themselves as chasing hard in the pack behind Wal-Mart," said Richard Lloyd-Owen, Deloitte's head of consumer business.
While Wal-Mart is dominant in the US, rival retailers have got a head start on it in some key emerging markets.
"Winning in places like China, India and Russia and not just a retailer's home market is going to be crucial in the future," Mr Lloyd-Owen added.
"In that sense, Tesco, Carrefour and Metro would probably say they have a level playing field with Wal-Mart."
US firms Kroger, Costco and Target, Dutch firm Ahold and Germany's Aldi complete Deloitte's list of the world's top ten retailers.
In a separate study, Deloitte found that US supermarket group Roundy's was the world's fastest growing retailer between 1999 and 2004, averaging 57% compound annual growth.
Internet retailer Amazon grew 33% during the period, making it the sixth fastest-growing firm.
This put it just ahead of British firm Morrisons, which got a huge sales boost from its acquisition of Safeway.