Returning home from some overseas travel, I saw an interesting table published in the International Herald Tribune that listed the 20 largest companies in the world by market value. The table, published July 9, listed each company's market value, most recent annual sales, and industry sector. It also provided me with a snapshot of which companies the world's investors value the most.

Once upon a time, you would have expected to scroll down a list like this and find the majority of companies headquartered the in United States. And although our domestic companies still represent a good portion of the world's best businesses, the list is beginning to evolve. Over the past few years, the globe has, in a business sense, flattened. And the list I'm about to discuss provides evidence of the growing number of international companies that dominate our world today.

With rising gasoline prices and the rapidly growing demand for oil, it isn't surprising that six of the top 20 companies are in the energy sector. While the U.S. continues to boast the No. 1 company on the list in Irving, Texas-based Exxon, its fellow energy competitors on the rest of the list are all international. Royal Dutch Shell, headquartered in the Netherlands, was ranked No. 5. PetroChina (NYSE:PTR), headquartered, as you might guess, in China, came in not far behind at No. 7. Right behind it at No. 8 was Russia's Gazprom. Further down the list were BP (NYSE:BP) from the U.K., and Total (NYSE:TOT) from France.

The U.S. did manage to fill the first four positions. Following Exxon was the venerable General Electric and was the only conglomerate on the list. Microsoft trailed GE as the sole technology company, and Citigroup came in fourth as one of five financial companies on the list.

But many new global faces fell in place after No. 4 this year. No, the U.K.'s HSBC (NYSE:HBC), or China's Commercial Bank of China or China Mobile (NYSE:CHL), haven't made it into the single-digit ratings yet, but their being on the list at all shows just how much our world is changing. The growing presence of foreign powerhouses also illustrates how important it is for investors to begin studying companies beyond their borders, so they can gain exposure to rapidly growing and profitable international companies.

It's still wise to be careful, though. I believe that some economies have experienced some irrational exuberance lately. For example, former U.S. Federal Reserve Chairman Alan Greenspan has warned that Chinese stock market gains are "clearly unsustainable" and has expressed his concerns that Chinese stocks are overvalued. Consequently, investors need to be reasonably educated about international economies before they begin picking stocks. Trying to become savvy about U.S. investing is tough enough, so the task of trying to follow and understand international companies may seem even more daunting. However, with nine of the 20 companies on the list based outside the States, it also seems foolish to overlook the potential growth from investing abroad.

If you don't feel confident enough to select individual companies around the world, there are many exchange-traded funds to choose from that will allow even a novice investor to gain international exposure. Two that quickly come to mind are the iShares MSCI EAFE Index (AMEX:EFA) and Vanguard's Emerging Markets ETF (AMEX:VWO).

Adding international stocks or funds to your portfolio can certainly add risk, since predicting continued success for many U.S. companies is usually much more straightforward than trying to analyze a foreign company and the economy in which it operates. But I believe the benefits outweigh the risks in the long term and will continue to add value to your portfolio as more and more international markets expand. Who would have guessed five or 10 years ago that three Chinese and one Russian company would make a top-20 list of global companies? And who's to say in the next five or 10 years that list won't progress into 20 non-domestic firms altogether? Stay tuned.

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Fool contributor Dr. Michael Cecil loves to travel the world but does not own any of the stocks listed in this article. If you would like to discuss this article, email him. Total is an Income Investor pick. Microsoft is an Inside Value recommendation. The Fool has a disclosure policy.