A comparative performance analysis based on design conditions has been made to give normalized algebraic expressions convenient to steady-state temperature and pressure predictions of a loop heat pipe (LHP). In analytical modeling of the LHP, a novel concept of pump efficiency is introduced to define the rate of heat loss or leakage through evaporator capillary wicks. Also introduced are general concepts of evaporator temperature effectiveness, condenser activeness, and subcooler temperature effectiveness. A simplified practical method is used to make a probable pressure loss estimate. The model was then mathematically evolved into a solution algorithm applicable to LHP off-design operation problems. In finding the solution, the radiation temperature is first calculated from specified heat load and sink conditions to give a possible condensation temperature, upon which other state variables are determined. Predicted thermohydraulic states are graphically shown in the figures to provide a better understanding of the operability of a commonly configured LHP. A few ground test results are also provided.