This study investigates the lean flammable limit (LFL) of CH4/air and CH4/CO2/air mixtures, using two different ignition devices: electrical discharge and laser-induced spark (LIS). The experiments were performed for CH4/air and (0.6 CH4+0.4 CO2)/air mixtures in ultra-lean conditions (0.48 phi 0.67) at different initial pressures (P=100-700kPa) and at an initial temperature of 298K. In these conditions, all observed flames were ascending. The minimum laser pulse energy for ignition (MPE) and the maximum overpressure (MO) were determined. The LFL increases with the initial pressure and with the addition of CO2.