Three commercial injection-molding-grade HDPE samples were evaluated for their properties. It was found that their impact property determined in the laboratory does not bear a simple correlation with the actual performance. The HTSEC study, undertaken to evaluate these samples, revealed that they differ significantly in z-average and z + 1-average molecular weights. This difference is attributed to the presence of a small amount of a very high molecular weight fraction and is responsible for the variation in the performance.