The material bucklings of twenty-five D2O moderated lattices of natural UO2 rod clusters were measured in the Process Development Pile (PDP). The measurements were made in one-region loadings, and should therefore be subject to little systematic error. A number of the lattices employed voided housing tubes around the fuel assemblies. Values of migration areas inferred from measurements of positive periods are also presented. An evaluation of the errors in the buckling measurements indicated that the bucklings should be accurate to about 1%. The migration areas are compared with theoretical values obtained from the Benoist theory, and the agreement is shown to be good.