Flow regime map is a very useful tool. Based on the defined dimensionless parameters, the correct flow regime can be found from the map. It is also a common practice that well proven heat transfer correlations are also provided in the flow regime map such that thermal engineers can immediately select the correct correlation for design purposes. Different flow regime maps were necessary to be established for different boundary conditions, different pipe orientations, and various pipe inlet configurations. For horizontal circular pipes fitted with three different inlet configurations (re-entrant, square-edged, bell-mouth) under uniform wall heat flux boundary condition, Ghajar and Tam [1] developed flow regime maps for the determination of the boundary between single-phase forced and mixed convection using experimental data [2]. Based on the ratio of the local peripheral heat transfer coefficient at the top and the bottom, the heat transfer data was classified as either forced or mixed convection among the different flow regimes. The forced-mixed convection boundary was then obtained by empirical correlations. In a recent study, Tam et al. [3] used an alternative approach called Support Vector Machines (SVM), to develop flow regime maps for the same set of data [2]. Three maps were developed for different inlet types. It was shown that SVM maps outperform the traditional maps. The disadvantage of the previous study is that the maps are not unified. It is of interest to establish a unified map for all types of inlet. Therefore, this study will extend the application of the SVM method to develop a unified flow regime map. The results show that the new unified flow regime map can classify the forced and mixed convection experimental data into different flow regimes with good accuracy. © 2010 American Institute of Physics.