I have seen the fuel of the future.It's not natural gas. That was the fuel of the future in 2000. It's not uranium. That might be the fuel of the future in 2015, if the new generation of nuclear plants turns out to be as good -- once someone builds one and operates it for a while -- as their proponents hope. It's not solar or wind or fuel cells, either. But they could give nuclear a run for its money by 2015 -- if government subsidies produce enough of a market to drive costs down further. Nope. The fuel of the future is coal. For the next five years anyway. My prediction is based on nothing more or less grand than this: Coal is cheap, and the coal supply is stable. I think investors can count on coal stocks, such as Peabody Energy ( BTU) and Arch Coal ( ACI), to continue to outperform the stock market -- on average -- for the next five years. An even better bet, however, are the shares of the companies that make the steam turbines that allow utilities to turn coal into electricity. I'd put General Electric ( GE), Germany's Siemens ( SI) and France's Alstom in that group. And, of those, Alstom would be my favorite. Exactly how cheap is coal? Really, really cheap when you compare it with other fuels used to generate electricity. In December, according to the investment bank Natexis Bleichroeder, U.S. coal sold for the equivalent (taking into consideration the different energy content of the two fuels) of natural gas priced at $3 to $4 per million BTUs. In December, the spot price of natural gas hit $15.50 per million British thermal units. On Jan. 19, after a monthlong selloff, natural gas sold for $8.59 per million BTUs. Even if the price of natural gas falls further -- to, say, $7 per million BTUs -- coal will still be about half as expensive as natural gas.