Molecular oxygen 16^O_2 is a key element in interstellar
 chemistry networks.  Because of interference of telluric oxygen
 it can only be observed by space telescopes.  However,
 due to its homonuclear nature, infrared transitions (magnetic
 dipole, electric quadrupole) are weak.
 A search is proposed for most promising sources:
 1) deep integration on the cool dense Sgr B2 cloud in two
    lines (138 and 165 micron) in case of a autumn launch,
 2) deep integration on Orion Pk1 (6.4, 119 and 138 micron)
    in case of a spring launch.
 Both observations should yield possible results for O_2 abundances
 being in a range as given in different chemical models and should
 allow to improve our knowledge of interstellar oxygen abundance
 and chemistry.