Jeff Bezos has re-entered the top 20 on Forbes' list of the world's billionaires, riding a wave that has sent Amazon shares soaring by more than 50 percent over the past year.

Forbes puts Bezos' wealth at $25.2 billion, a fortune more than $2 billion greater than that of the list's next two entrants, Google's Larry Page and Sergey Brin.

Google shares, of course, have also been on a tear, blowing through $800 to reach an all-time high last month. Though Amazon's stock price, adjusted for splits, has yet to break $300, its gains have topped even Google's, which is up by about one-third compared to the same time last year.

Forbes says this year is the first time Amazon's founder has made the billionaires' top 20 since 1999, when his company was riding the first internet bubble. Amazon plodded along unremarkably for several years after the bubble burst. In retrospect, Bezos appears to have spent those fallow years figuring out how to transform Amazon from dotcom fad into the formidable retail force it is today, to the benefit of shareholders and his own net worth.

Still, Amazon has plenty of critics who contend that the company's current stock market success stems from Amazon-specific irrational exuberance. Its $61 billion in sales last year make Amazon one of the world's biggest retailers, online or off. Yet the company failed to turn a profit for the year.

Amazon competes on selection and price. For years, Amazon appears to have been able to undersell brick-and-mortar retailers because it lacks the overhead that comes with having to maintain physical stores. But Amazon stock bears argue the company's red ink shows that Amazon's low prices are an illusion that undercut its own business. To turn a profit, they say, Amazon's prices will have to rise.

If Amazon's prices do go up, its steady encroachment on its chief rival, Walmart, will falter, as will Bezos' hopes of climbing past no fewer than four Walmart heirs all ranked higher than him on Forbes' list of the world's richest. He also has a long way to go to best his Seattle-area neighbor: Bill Gates ranked number two just behind Mexico's Carlos Slim with an estimated fortune of $67 billion.