A special modified tensile creep test was used to investigate the stress cracking behavior of various high-density polyethylenes (HDPE). Blends of HDPE with other HDPEs, with linear low-density polyethylene (LLDPE), and specifically with various slightly long-chain branched linear low-density polyethylenes (HBPE) were tested for their failure times. Whereas HDPE blends, including higher-molecular-weight HDPE components, yield only a minor improvement in stress cracking resistance, a considerable improvement was produced when an LLDPE weight fraction of 0.3 or more was used. Adding HBPE also improves the environmental stress cracking resistance. Environmental stress cracking resistance improves with increasing HBPE content, and, for a constant HBPE concentration, it increases with increasing octene content of the HBPE. Adding HBPE, with a low octene content, however, results in reduced failure times of the blend compared with HDPE blends that exhibit relatively good environmental stress cracking behavior. The results are explained in terms of the tie-molecule density.