The functionalization of three n-alkanes by means of a lon-pressure oxygen plasma has been achieved The plasma was generated by applying a low-frequency high-voltage glow discharge through an oxygen flow. The activated species so produced have been allowed to interact with the surface of each one of the liquid compounds at a time. The hydrocarbon has been cooled down to a temperature low enough so that its vapor pressure is about 20-100 times lower than the O-2 pressure, this being of the or der of 0.1-0.4 torr. Under, these conditions the main products of the reactions have been the alcohols, except for the primary, ones, and tire cor responding ketones. A remarkable result Ile have arrived at is that for the first time secondary carbon-hydrogen bonds have shown to possess different reactivities with O(P-3). Tire latter has proved to be the most relevant active species of the plasma. A discussion is given to explain this novel result under two theoretical bases recently published (i) a conformational analysis of the hydrocarbons according to molecular mechanics calculations, and (ii) an analysis of properties of the molecules based on calculations with charge distributions derived from 6-31G* wave functions.