Investing is scary these days. Is it safe to go back in the stock market? Is the bond market the place to be? With so much uncertainty, how can investors know where to put their money? Morningstar, the mutual fund research service, is on to an answer, but it might not make you feel better about your financial advisers.

In a study released last week, Morningstar found that low fees are the most dependable indicator of a mutual fund’s future performance. Morningstar looked at fees and performance during various time periods from 2005 through March 2010. Over every period and in every asset class  domestic equity, international equity, balanced, taxable bond and municipal bond  the cheapest funds, as a group, produced higher total returns than the most expensive group.

We’re not talking loose change. Domestic equity funds in the cheapest group in 2005 returned an annualized 3.35 percent over the next five years, versus 2.02 percent for the most expensive group. The gap was similar in other asset categories.

Given the importance of fees, it is heartening that the Securities and Exchange Commission now requires mutual funds to prominently report expense ratios, the percent of assets consumed each year by operating costs. The rules need to be tighter, however, to ensure that salespeople give investors the data before making a sale. In another step forward, the S.E.C. has begun to develop a rule to cap 12b-1 marketing fees, long viewed by investor advocates as excessive and misleading.