Arrays of heat pipes placed in soil may be used to good advantage for cooling or heating equipment. This paper gives results of a study that included the coupling of heat pipe thermal characteristics with soil thermal characteristics for such applications. A transient mathematical model was developed for the combination that accounted for thermal capacitance and resistance of the individual heat pipes, the number and arrangement of heat pipes in the soil, and soil properties. The model was verified by comparing it with published experimental and analytical results. Parametric studies were then performed, and the results were used to develop some correlation equations that may be used to predict the thermal performance of arrays of heat pipes in soil. The dependence of spacing, type of array, heat pipe properties, and soil properties is included in the simple correlation equations.