The growth of funds designed to mimic the price of crude oil and other energy futures is reminiscent of a similar craze that precipitated the stock market crash of 1987, billionaire financier George Soros told lawmakers Tuesday. The surge in popularity of commodity index funds is "intellectually unsound ... and distinctly harmful in its economic consequences," Soros told a US Senate hearing. When speculators enter a market mostly on one side - in this case, betting on rising oil futures - it "distorts the otherwise prevailing balance between supply and demand." He likened it to the rush to invest in portfolio insurance more than 20 years ago. When those investors tried to exit the market at the same time, stock markets around the world crashed. While acknowledging he was not an expert on oil markets, Soros said he has spent years studying market "bubbles" that begin with a trend based in reality, but are then followed by some misinterpretation of that data. He sees no imminent crash in oil prices, however, and said a decline in consumption will not occur unless the US and other developed nations' economies fall into recession.