Abstract <p>A two-rotor external compression vacuum pump with four-blade rotors is considered. Equations for the primary and secondary components of the elliptical rotors are presented. The characteristics of the profile in molecular gas flow are analyzed. Angular coefficients are used to calculate the throughput of the rotor mechanism and individual gaps. The coefficients characterizing the efficiency of the pump profile—the utilization of the working volume and the throughput of the channels in the rotor mechanism—are expressed as a function of the ratio of the bore radius to the distance between the rotor axes. The limits on profile design and the optimal ratios of the rotor parameters ensuring the best performance are determined.</p>