Further development and verification of the author’sgeneral correlation is presented. While this correlation isalso applicable to vertical tubes, only horizontal tubes areaddressed in this paper. The boundary between the mixedand laminar heat transfer regimes for horizontal tubes washitherto undefined. An equation to determine this boundaryis presented. The relation between these heat transferregimes and flow pattern regimes is investigated. The correlationis compared to additional data for horizontal tubes,which include very low flow rates and fluids not included inthe earlier paper. A total of 547 data points from 11 studiesare analyzed. The data include CO2 near critical pressureas well as seven other fluids. Together with the previouslyanalyzed data for all orientations, this correlation has beenverified with 1736 data points from 51 studies that include24 fluids.