We report the results of ion-exchange experiments conducted on 17 commercial soda-lime-silicate (SLS) float glass and 8 experimental SLS glass compositions. A significant variation in the depth of K+ penetration with relatively small changes in composition was observed. The data were fit to a multiple regression model in which the major oxides are the independent variables and depth of K+ is the dependent variable. The model indicates that increased depth of exchange (increased interdiffusion coefficient) correlates predominantly with increased K2O and/or Na2O content of the glass, with a decreased total alkaline earth content and with the ratio of CaO/MgO.