In computer simulations we carried out of dispersion in fluid flow in cylindrical beadpacks, it appeared that the longitudinal dispersion coefficient, DL, was dependent on the ratio of the cylinder radius to bead diameter (R/d) much more than was indicated in the literature, where it was postulated that for R/d greater than 5 the dispersivity would be independent of R/d. Since the computer simulations were limited to relatively small systems, one couldn't be certain that our results were not the result of a small sample approximation. Thus, we investigated dispersion using the approach Aris used in his analysis of Taylor dispersion in tube flow. Predictions of this analysis indicated a strong dependence of dispersivity on R/d at ratios well above R/d=5. This last summer, we carried out experiments on beadpacks with R/d = 9.5, 12.5 and 25.4. We found a strong dependency of DL on R/d, in close agreement with the analysis.