OPERA is one of the two detectors foreseen in the CERN Neutrino to Gran Sasso project, devoted to the detection of νμ into ντ oscillations in the parameter region suggested by SuperKamiokande data on atmospheric neutrinos. Bakelite RPCs will be used to instrument the iron yoke of the muon spectrometers. We present the results of long-term (greater than 6 months) streamer operations of real size OPERA RPCs at cosmic rays fluxes. Given the very low rate observed in the underground Gran Sasso Laboratories, under 3km w.e., even this short time period is equivalent to more than 10 OPERA years. Results of tests with different gas mixtures are reported, in view of decreasing the streamer charge of operation for the RPCs employed in the experiment.