Most corporations of a certain size can't wait to sell their shares on a stock exchange, given the influx of cash and recognition that accompanies an initial public offering. But some things are just too good to share. Other corporations prefer to grow internally, eschewing the public trading of their shares altogether. The advantages to staying private are stark - no reporting requirements, no disassociated shareholders to please, no undue focus on short-term goals. When run sharply, private companies can grow to sizes rivaling those of their largest publicly traded counterparts.

First, a Definition

Determining the world's most valuable private companies largely depends on how you define "private." By some rationale, any company that doesn't trade publicly would count. But atop that list would be Saudi Aramco, which was founded in the 1930s as a subsidiary of America's publicly traded Standard Oil (forerunner of Chevron.) Once Saudi Aramco became profitable in 1950, the Saudi king graciously let Standard Oil keep half the profits while expropriating the rest. The alternative was to have the government simply commandeer the entire company, which it did anyway in 1980.

So best to call Saudi Aramco a state-owned enterprise (along with other giants such as China Mobile and Petrochina), and restrict ourselves to companies that grew out of private-sector ingenuity and continue to flourish as such today.

Turning Wheat into Bread

While the title of America's largest public company has changed over the last couple of decades, from General Motors to Microsoft to ExxonMobil, the most valuable private American company has enjoyed its status largely unchallenged. Cargill is a $27 billion company that you probably have only scant familiarity with, yet have almost certainly patronized. The Minnesota multinational is responsible for a staggering one-quarter of all the grain exports from the United States.

Only a dozen or so American public companies earn more revenue than Cargill and few have its international scope. Cargill operates in 65 nations, on every populated continent, employing 142,000 people. It imports almost one-quarter of all the beef that enters the United States. When you add up all Cargill's interests, everything from phosphate production to energy trading, it totals over $100 billion revenue, annually.

So who does own Cargill? The Cargill family, of course. The understandably secretive Cargills own 90% of the conglomerate, and no, they haven't disclosed any plans to sell anytime soon.

Have a Koch and a Smile

Of slightly smaller size but similar influence is Koch Industries, which is also large enough to rank among the 20 largest public companies in the United States. The company was founded by family patriarch Fred Koch, a chemical engineer who in 1927 developed an efficient way to refine crude oil into gasoline. 85 years later, the company maintains a presence in refining but has expanded into fields as diverse as polymers and ranching. The Wichita-based Koch's most famous subsidiary is Georgia-Pacific, one of the world's largest pulp and paper manufacturers.

Fred Koch died in 1967, willing the company to his four sons. In 1983, brothers Charles and David bought out Fred Jr. and William for what certainly sounded like a generous amount at the time - $1.1 billion. Charles and David each own 42% of the company today, and it's safe to say they'll give thought to selling their interest right around the same time the Cargill clan does.

Out of the Box

Large private companies aren't exclusive to the United States. Europe's most formidable include a Swedish furniture manufacturer (and doubtless the world's biggest popularizer of Allen wrenches), founded in 1943. With net shareholders' equity of $23 billion, IKEA has never strayed from its original business. Today the company operates hundreds of stores in dozens of countries, bringing simple functionality and casual minimalism to the masses.

The multinational's teenage founder, Ingvar Kamprad (the "IK" in IKEA), is now 86 and lives in Switzerland. In 1982 he created a charitable foundation to own the bulk of the company, which it's done ever since. A complete breakdown of IKEA's ownership structure would entail several thousand words, but to summarize, Kamprad's Stichting INGKA Foundation owns the holding company that owns 90% of IKEA's stores. A separate IKEA-branded company owns yet another holding company that owns IKEA's intangibles (trademark, etc.). That company is owned by yet another foundation, founded by Kamprad and based in Liechtenstein, that is saving IKEA millions of dollars in taxes every quarter.

The Bottom Line

As a rule, the successful private companies are the large ones. And the large ones are the ones that consistently reinvest their profits. With no need to worry about paying out dividends, buying back shares on the open market, or other gimmickry that would help make their companies more attractive to potential shareholders, private companies enjoy flexibility and adaptability that most public companies can only dream of.