In this study, a thermodynamic analysis of a hydraulic braking energy recovery system used in vehicles is performed for newly developed systems. The present system is related to the field of energy efficiency in vehicles. The energy recovery system comprises a first pump, a hydraulic accumulator, and a hydraulic motor. The first pump is a variable displacement hydraulic pump (VDP). The hydraulic accumulator is connected to the first pump which operates to store hydraulic fluid under pressure. The hydraulic motor is hydraulically connected to the accumulator to receive hydraulic fluid. The motor is adapted to drive a second hydraulic pump, which is hydraulically connected to the auxiliary system, using hydraulic energy stored in the accumulator. The overall charging and discharging efficiencies, and the overall system efficiency is calculated and presented in this paper. For the purpose of the analysis, EES (engineering equation solver) is used. In addition, parametric studies are performed to observe the effects of different substantial parameters, namely, the inlet pressure and temperature of the accumulator, and the reference environment temperature, in order to investigate the variations in the system performance in terms of the efficiencies. Two systems are developed and it is found that the charging and discharging efficiencies for one system are 83.81% and 87.73%, while for the other system the charging and discharging efficiencies are 81.84% and 85.67%, respectively.