Gains in photonic crystal (PC) lasers are analyzed using a modified complex plane-wave expansion method with temperature and frequency-dependent dielectric constants. The analysis is performed for 0.78 mu m GaAlAs lasers with one- and two-dimensional PCs. We have presented the modal gain of each photonic mode in the PC as a function of wavevector. Further, the variations of this gain dispersion with temperature are shown for the first time. Our calculated results clearly explain the experimentally obtained temperature range of PC mode oscillations. This study will be useful for the design of PC lasers that are robust with respect to changes in temperature. (C) 2012 Elsevier Ltd. All rights reserved.