Vibrational relaxation in methane-oxygen mixtures has been investigated by means of a time-resolved pump-probe technique. Methane molecules are excited into selected rotational levels by tuning the pump laser to 2 nu(3) lines. The time evolution in population of various vibrational levels after the pumping pulse is monitored by probing, near 3000 cm(-1), stretching transitions between various polyads like 2 nu(3)(F-2) - nu(3), (nu(3)+2 nu(4)) - 2 nu(4), and (nu(3)+nu(4)) -nu(4) transitions. Measurements were performed from room temperature down to 190 K. A numerical kinetic model, taking into account the main collisional processes connecting energy levels up to 6000 cm(-1), has been developed to describe the vibrational relaxation. The model allows us to reproduce the observed signals and to determine rate coefficients of relaxation processes occurring upon CH4-O-2 collisions. For the vibrational energy exchange, the rate coefficient of transfer from O-2 (v = 1) to CH4 is found equal to (1.32 +/- 0.09) x 10(-12) cm(3) molecule(-1) s(-1) at 296 K and to (1.50 +/- 0.08) x 10(-12) cm(3) molecule(-1) s(-1) at 193 K.