Experimental results from the present study show substantial, independent Mach number effects (as the Reynolds number is held constant) for an array of impinging jets. The present discharge coefficients, local and spatially averaged Nusselt numbers, and local and spatially averaged recovery factors are unique because (i) these data are obtained at constant Reynolds number as the Mach number is varied, and at constant Mach number as the Reynolds number is varied, and (ii) data are given for jet impingement Mach numbers up to 0.74, and for Reynolds numbers up to 60,000. As such, results are given for experimental conditions not previously examined, which are outside the range of applicability of existing correlations. (c) 2006 Elsevier Ltd. All rights reserved.