We report new observations of molecular oxygen in absorption at z = 0.685 in front of the radio source B0218+357 .
The lines at 56.3 and 118.7 GHz have been observed , redshifted to 33.4 and 70.5 GHz respectively , with the 12m at Kitt Peak , 43m at Green Bank telescopes , and the 45m Nobeyama radio telescope .
Deriving the surface filling factor of the absorbing dark cloud with other lines detected at nearby frequencies , we deduce from the upper limits on the O _ { 2 } lines a relative abundance of molecular oxygen with respect to carbon monoxyde of O _ { 2 } /CO \la 2 10 ^ { -3 } at 1 \sigma , seven times lower than the previous limit .
The consequences of this result are discussed .