Cooling　curves　of　ten　different　quenching　oils　were　obtained　and　the　hardness　of　test　specimens　quenched　in　these　oils　was　determined.　It　was　shown　that　the　hardening　power　calculated　from　the　Segerberg　equation　provided　better　agreement　with　test　results　than　the　transition　temperature　from　vapor　stage　(full-film　boiling)　to　the　nucleate　boiling　stage　and　the　maximum　cooling　rate.　The　hardening　power　equation　also　provided　better　agreement　with　respect　to　hardness　for　carbon　steel　than　for　alloy　steel.　The　development　of　revised　hardening　power　equations　for　carbon　and　alloy　steels　showed　that　there　is　an　alloy-dependent　optimal　quenching　temperature　range,　and　it　was　concluded　that　the　newly　developed　equations　reported　here　are　superior　to　the　single　equation　previously　published　by　Segerberg　to　quantify　the　quench　severity　provided　by　a　quenching　oil.　A　methodology　to　assess　data　set　correlation　is　proposed　and　illustrated.　©　2009　by　ASTM　International,.