Long term performances of OPERA bakelite RPC system

OPERA is an experiment dedicated to the observation of νμνμ into ντντ oscillations through ττ appearance exploiting the CNGS beam. The experiment is composed by two identical super-modules, each with a target section (made of emulsion/lead bricks alternated with a scintillator Target Tracker) and a muon spectrometer (instrumented with bakelite RPCs and drift tubes).The RPCs are operated in streamer mode with the gas mixture Ar/C2H2F4/isoC4H10/SF6=75.4/20/4/0.6. The present performances of the RPC detectors are presented and the aging status of the system after four years of operation is described. The sample of events induced by the CNGS neutrino beam as well as a large sample of cosmic rays have also been used to study general properties of streamer-operated RPCs.