Being in a boom-and-bust sector, could energy stocks be on the verge of a bust after such a big boom?
Natural resource funds tracked by Morningstar are the top-performing sector this year, gaining 30.21% going into Thursday. They've cranked out an average annual 26.7% the past three years and 30.1% the past five years.

"Natural resources and commodities have seen a tremendous run over the last five years, but we still think this cycle could extend well into the next decade due to strong demand growth in emerging markets," said Evan Smith, co-manager of U.S. Global Investors Global Resources (NASDAQ:PSPFX - News). "The cost of producing oil is becoming greater, and access to easily produced oil is becoming more difficult."

China and India together are responsible for 45% of the increase in global energy demand, according to an outlook released last week by the Paris-based International Energy Agency. Their energy use is set to more than double between 2005 and 2030.

Oil imports for these emerging markets are expected to jump about 300% between 2006 and 2030 to 19.1 million barrels a day, surpassing the current combined imports of the U.S. and Japan. Most of the