The crystal structure, superconducting properties and oxygen stoichiometry of room temperature chemically oxidized La2-xSrxCuO4+y (x = 0.05, 0.09) have been studied by means of powder neutron diffraction, magnetic susceptibility and thermogravimetric analysis. The presence in these materials of interstitial oxygen located at (1/4, y, 3/4; y almost-equal-to 1/4), as previously observed in oxygen-rich La2CuO4+y, is proposed from neutron diffraction data at different temperatures. This is supported by the excess of mass loss detected by TG for the oxidized materials relative to the starting ones. Besides, an important improvement in the superconducting properties (T(c) and superconducting volume fraction) of these compounds is observed after oxidation. On the other hand, no phase separation into two phases with different oxygen content is observed at low temperature.