One of the main factors that influence the operating temperature of a loop heat pipe (LHP) is the distribution of a working fluid in the device. The paper presents the classification of LHP operating modes on the basis of the criterion of presence or absence of the working-fluid vapor phase in the compensation chamber (CC). It gives a description of method of calculating the LHP operating temperature for every operating mode and shows the characteristic features, advantages and disadvantages of every mode. (C) 2006 Elsevier Ltd. All rights reserved.