Experiments were performed to analyze dilution effects of CO2, N2 (thermally inert), or Ar (chemically inert) injected in air side, on non-premixed CH4/air flames. The flow rate ratio (Qdiluent/Qair)lifting controls lifting process. Anchored flames stabilize more downstream as Qdiluent/Qair increases; under given aerodynamic conditions, the attachment height, Ha vs.(Qdiluent/Qair)/(Qdiluent/Qair)lifting follows a unique profile whatever the diluents. Flames lift off when Ha,lifting, unique value for different diluents, is attained. Flame bases turn blue by adding a diluent, caused by a reduction in soot formation (see LII images), largely marked at low velocities. It is particularly drastic with CO2. For naturally lifted flames, liftoff height (HL) increases by adding diluents too. Liftoff phenomenon, dependent on (Qdiluent/Qair)lifting, leads to a unique HL-evolution with (Qdiluent/Qair)/(Qdiluent/Qair)lifting for different diluents.