By David Sterman

NEW YORK ( StreetAuthority ) -- Oil, technology, minerals and banking. Those are the industries that are host to the world's most richly-valued companies. In fact, with a market cap of more than $250 billion, these companies are larger than the gross domestic product of countries such as Portugal, Egypt or Chile.

I'll tell you how you can profit from these titans of industry in a minute, but first, take a look at the five most valuable stocks on the planet.

Joining this exclusive club is quite an honor, but you can be kicked out at any time. GE ( GE) was worth roughly $600 billion a decade ago, the biggest company in the world at the time, and now it doesn't even rank in the top 10. Microsoft ( MSFT) eventually overtook GE, but has since fallen to No. 6 in the world.

Just below Microsoft resides Brazil's energy titan Petrobras ( PBR) and the China Construction Bank isn't far behind. My colleague Ryan Fuhrman thinks Petrobras could be the first $1 trillion stock

The fact that four of the nine largest companies in the world reside in China or Brazil should tell you we live in a changed world.

How will this list look five years from now? Well, a look at each of the top companies' prospects gives us a good idea about tomorrow's titans -- and how you can profit.

1. ExxonMobil (XOM)

The odds are against this energy company retaining its top spot, for one simple reason: buybacks. Shares outstanding peaked at 6.9 billion and have been falling ever since, to less than five billion currently. Management intends to stick with that plan, and the share count could fall below 4 billion in the next five years.

Shares would need to rise about 25% simply to offset that trend, and that's not assured because this is now a slow-growth company. (2010 sales are likely to be on par with sales levels back in 2006). Then again, a fresh "Super-spike" in oil prices would give a solid boost to shares. But surging oil prices have a way of creating conditions for a pullback as demand gets choked off.

Prediction: ExxonMobil's market value will be less than $400 billion five years from now.

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