  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 O2
lines a relative abundance of molecular oxygen with respect to carbon monoxyde
of O2/CO $\la$ 2 10$^{-3}$ at 1$\sigma$, seven times lower than the previous
limit. The consequences of this result are discussed.
