A simplified one dimensional single phase model for an oil pebble thermal energy storage system is used to examine the thermal performance of three solid sensible heat pebble materials. These are fused silica glass, alumina and stainless steel. The model is validated with experimental results and reasonable agreement is achieved between experiment and simulation. The thermal performance of these materials is evaluated in terms of the axial temperature distribution, the total energy stored, the total exergy stored and the transient charging efficiency. The results indicate that not only is the value of the total amount of energy stored important for the thermal performance of oil-pebble-bed systems but also that the amount of exergy stored and the degree of thermal stratification should be considered. A high ratio of the total exergy to the total energy stored is suggested as a good measure of the thermal performance of the pebble material. (C) 2008 Elsevier Ltd. All rights reserved.