Class B shares of mutual funds consistently underperformed both Class A and Class C shares over trailing three- and five-year periods and maintained the highest expense ratio of the three share classes, according to a recent Standard & Poor’s study.

S&P queried data from its more than 15,000 domestic mutual funds and adjusted the shares for sales charges. The firm found that Class B shares also lagged Class A shares over the trailing 10 year period, while matching that of Class C shares over that time. The report concluded that B shares’ third-place status was related to having an average back-end load of 4.5%.

As for the expense ratio, B Shares maintained a 2.05%, just a fraction ahead of the 2.04% showed by Class C shares, and significantly behind the 1.35% shown by Class A shares.

"Class B shares frequently convert to A shares prior to being held for ten years, so they often are not the best option for investors with that time horizon given their higher expenses," said Rosanne Pane, mutual fund strategist at S&P, in a statement.

Investors in B shares don’t charge a sales commission up front, charging only when an investor sells his/her shares. Even then sometimes the investor doesn’t pay a sales charge, but this share class typically has higher ongoing expenses, a tradeoff that can end up costing investors in the long run.

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