Oxygen is the third most abundant element in the universe. In the gas phase of the interstellar medium, oxygen is believed to be found principally in the species such as O, O2, CO, OH and H2O. From the present observations of the ISM it seems that none of these molecules could account for the bulk of the gas- phase oxygen. What is the major depository of the gas-phase oxygen in the cold component of the ISM is still one of the outstanding open question in interstellar chemistry. Recent observations from KAO and more unambiguously from ISO showed the evidence of OI 63um absorption in galactic molecular clouds - HII region complexes. This important result shows that a considerable column density of atomic oxygen is present along the line of sight of such complexes. Observations with ISO LWS grating (unresolved lines) of ultra compact HII regions, as well as of high mass Pre-Main sequence objects, show a ratio of the OI (63um) to OI (145um) which can be explain only if a strong absorption of the OI 63um is present. Furthermore, LWS FPs observations of the OI broad emission line from the galaxy M82 have been performed. The line is clearly resolved by the LWS FP and exhibit a strong feature in absorption, likely unresolved, at the rest wavelength of the OI line. This result would indicate that absorption by atomic oxygen should be mainly due to diffuse galactic clouds along the line of sight to M82. This proposal intends to study the actual distribution of atomic oxygen, in its ground state, from the OI line seen in absorption against a selection of bright sources in the galactic plane and a few at higher galactic latitudes. The main goal is to derive the quantity of oxygen in its atomic form within the galactic ISM. The sources have been chosen also to be at a range of galactocentric radius to study a possible variation of the OI absorption at large scale in the Galaxy. Several sources of each type (giant molecular cloud - HII region complexes, Pre-main sequence star and ultra compact HII regions) are requested to be observed to check the possibility for some of these to present an OI absorption coming from cold material associated with their surroundings, rather than from the diffuse medium on the line of sight.