This paper describes an experimental apparatus to study heat transfer and pressure drop of liquid-cooled offset fin compact heat exchangers (cold plates). Liquid coolants used in the test are water and polyalphaolefin, for which the Prandtl number ranges from 3 to 150. From the comparison with previous air-cooled models, the liquid-cooled experimental data show that the Prandtl number has a large effect on the Nusselt number of the offset fin geometry. A numerical heat transfer analysis was performed to investigate the surface temperature distribution and uniformity of heat flux in the cold plates. The results demonstrate good agreement with experimental surface temperature measurements. The model results were used to guide data reduction procedures. In particular, significant end effects are predicted. Through experience with the heat transfer model. these end effects were isolated.