ESDU 92003 recommends the Petukov equation for the prediction of the heat transfer in single-phase Newtonian flow, following a comparison of it and five other correlations with a database of nearly 800 experimental results extracted from the literature. The quality of the fit of the data with the six correlations is tabulated in various flow regimes defined by specific ranges of Reynolds and Prandtl numbers. The correlations are also compared as graphs of Nusselt number against Reynolds number for values of Prandtl number of 0.7, 10 and 100. Two forms of the equation are given, one applying in the higher ranges of Reynolds and Prandtl numbers. Corrections for variable fluid properties are suggested for liquids as a function of bulk-to-wall dynamic viscosity ratio and for specific gases in terms of bulk-to-wall temperature ratio. Information on regimes for forced, free and mixed convection for both horizontal and vertical flow is included. The Petukov equation may be applied provided the thermal entrance length is exceeded and values for that are given based on local or mean Nusselt number. Worked examples illustrate the use of the correlation.