Redox Reactions - Oxidation and Reduction, Gain or Loss of Oxygen
[Oxidation is a gain in oxygen, or a loss of hydrogen]
hence, any combustion process is classified as oxidation, as it involves a gain in oxygen.
methane + oxygen -> carbon dioxide + steam
CH4 (g) + 2 O2 (g) -> CO2 (g) + 2 H2O (g)
when methane burns, the carbon atoms in methane gain oxygen and therefore is oxidised.
alternatively, this can be seen as methane losing hydrogen atoms, which is again oxidation.
[Reduction is a loss of oxygen, or a gain in hydrogen]
which is the opposite of oxidation. =P