Resonances in the current‐voltage characteristics of interferometers with two Nb‐NbOx‐Pb window junctions have been experimentally investigated. The data are compared with the theoretical curves computed both for the voltage and for the magnetic field dependence of the resonance amplitudes. Very good agreement is found in all the range of values of the damping parameter &Ggr;=I0R/Vr, whereVris the resonant voltage andI0andRare the maximum Josephson current and the parallel resistance of each junction. New features that cannot be explained in terms of the existing theory have been observed in devices with larger values of the parameter &bgr;=2&pgr;LI0/&Fgr;0, whereLis the loop inductance, and &Fgr;0is the flux quantum.