On 20 September 1999, the Ms7.6 Chi-Chi earthquake ruptured the Chelungpu fault in central Taiwan. Integrating observed and inversed results of source parameters, the fracture energy, Eg, and frictional energy, Ef, on the fault and its northern and southern segments are estimated. Together with given values of strain energy, ΔE, and seismic radiation energy, Es, the seismic efficiency, i.e., η = Es/ΔE, and the radiation efficiency, i.e., ηR = Es/(Es + Eg), are evaluated. The average fracture energy per unit area, G, is also calculated from Eg. The frictional heat caused by dynamic frictional stress is calculated from Ef. Results show a marked difference in source properties between the two segments. The average frictional and ambient stress levels on the two segments are estimated. The total energy budget of and heat generated by the earthquake are elucidated based on a two-dimensional faulting model with frictional heat. Both observed and calculated results suggest the possible existence of fluids, which produced suprahydrostatic gradients, on the fault during faulting. Lubrication and thermal fluid pressurization might play a significant role on rupture.