Most corporations of a certain size can't wait to "go public" and 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.

Many other corporations prefer to grow internally, eschewing the public trading of their shares altogether. These private companies have certain stark advantages: no reporting requirements, no disassociated shareholders to please, and no undue focus on short-term goals. But don't be fooled: some of the largest companies are private companies, and when run sharply, private companies can grow to sizes rivaling those of their largest publicly traded counterparts. So what are the world's top three largest private companies?

Defining Private Companies

Determining the world's most valuable private companies largely depends on how you define "private." By some rationales, any company that doesn't trade publicly would count. Using that definition, the world's largest private company 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.

As a result, it's best to exclude state-owned enterprises such as Saudi Aramco, along with other giants such as China Mobile and Petrochina. Instead, standard lists of most valuable private companies are best restricted to companies that grew out of private-sector ingenuity and continue to flourish as such today.

The World's Largest Private Company

While the title of world's largest public company has changed over the last couple of decades, from ICBC to JPMorgan Chase to Apple, the most valuable private American company has enjoyed its status largely unchallenged. Cargill is the most valuable private company in the world, valued at $55 billion. It is a company that you probably have only scant familiarity with, yet have almost certainly patronized. The Minnesota multinational is responsible for a staggering 25% of all 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 70 nations, on every populated continent, employing 155,000 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 $120 billion revenue, annually.

So who owns Cargill? The Cargill family, of course. The understandably secretive Cargill owns 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. Eighty-five 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.

Private Companies Abroad: IKEA

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 is not publicly traded and is another of the world's largest private companies, never straying from its original business.

Today, the furniture and home goods 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 most successful private companies are the large ones. And the largest private companies are the ones that are consistently reinvesting 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. Cargill, Koch Industries, and IKEA would know.