A novel compression strategy for air hybrid engines is proposed utilizing two storage tanks which increases the efficiency of regenerative braking of air hybrid vehicles significantly by increasing the stored air mass and, consequently, the storing pressure in the tank. The second law definition for efficiency is suggested and employed to evaluate the regenerative system capability in storing the kinetic energy of a decelerating vehicle. The maximum energy storing capacity of conventional and proposed compression methods are derived and the advantage of the double-tank system in increasing the energy storing capacity is shown. An experimental setup has also been designed and tested to evaluate the double-tank compression strategy in practice. The experimental results show at least 70% improvement in storing pressure and 125% improvement in energy storing capability in the regenerative braking process using the double-storage system.