Wynn didn't laugh, and the relationship between the billionaire casino moguls has only grown icier.

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Las Vegas apparently isn't big enough for this pair. Adelson complains eruptions from the Mirage's fake volcano are too loud. Wynn counters Adelson isn't building enough parking at his Las Vegas projects and the overflow snatches spaces from his own customers. (See: "The Gambler.")

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Their stormy rivalry shows that the world's richest can be just as contentious as everybody else. The difference is that when they feud, the ante is upped exponentially, putting companies or entire industries at stake.

Although some of the disagreements between Adelson, chairman of Las Vegas Sands (nyse: LVS - news - people ), and Wynn, chairman of Wynn Resorts, may seem petty, the risks couldn't be higher.

The latest battlefield: Macau, where each has casinos with big profits and bigger potential. The region, a magnet for Asian gamblers, long passed Las Vegas as the world's top gambling destination.

Often, the focus of a billionaire feud is a company. The relationship between two of France's richest moguls, Bernard Arnault and Francois Pinault, never recovered after both pursued Gucci.

Pinault eventually beat out Arnault for the luxury leather-goods maker but only after an acrimonious spat that featured defamation lawsuits and accusations of bribes.

A new tug-of-war is brewing in Europe between Irish billionaires Denis O'Brien and Anthony O'Reilly.

Cellphone magnate O'Brien began aggressively building a stake in Independent News & Media in 2006. He quickly revealed he was no fan of the Dublin-based newspaper publisher's current management, particularly Chief Executive O'Reilly.

O'Brien put it bluntly: "Tony O'Reilly would be better off retiring." O'Reilly knows how to take a hit though. The former rugby player's company recently questioned if O'Brien isn't just trying to settle an old grudge. They point to articles from Independent News titles about an investigation into whether any corruption occurred in the awarding of a mobile license to one of O'Brien's old companies.

When two remarkably successful businessmen have differing opinions on the best way to run something, it's no surprise that neither wants to budge. They got where they are by being right most of the time.

This self-assurance can turn some of even the strongest billionaire friendships into feuds. The business relationship between billionaires Barry Diller and John Malone stretches so far back that Malone calls it a marriage. Now they're heading for divorce.

The partnership grew increasingly strained as the two disagreed over how to manage struggling IAC/InterActiveCorp (nasdaq: IACI - news - people ), owner of home shopping network HSN and event-planning Web site Evite.

Diller, a former Hollywood executive, is chairman and chief executive of the company. Malone owns a big chunk of IAC stock.

The duo turned to the lawyers when Diller decided to break up IAC. Malone is against the plan, which will drastically reduce his voting power. The fate of a company with more than $6 billion in annual sales hung in the balance. Friday, a Delaware judge sided with Diller and said he could proceed with the breakup.

Even when the dispute between billionaires is only sporting, watch out.

Larry Ellison, the chief executive of Oracle (nasdaq: ORCL - news - people ), and Ernesto Bertarelli, a Swiss pharmaceutical billionaire, are going head-to-head for a boat race. Not some local regatta, mind you. This showdown is over the America's Cup.

The Cup is the world's most prestigious sailing trophy--and the most expensive race to enter. Building a super-fast yacht and hiring a skipper and crew can push costs over the $100 million mark.

Ellison and Bertarelli are racking up substantial legal bills as well. So far, they've spent more time in court than on the water as each tries to dictate the rules for the 33rd run of the event. A judge finally ruled this month that Bertarelli's Alinghi team and Ellison's BMW Oracle Racing will settle everything in a rare one-on-one duel.

Should be exciting. But first they'll need a court to decide on dates for the best-of-three series.