  We have observed 70 galaxies belonging to 45 Hickson compact groups in the
CO(1-0) and CO(2-1) lines, in order to determine their molecular content. We
detected 57 galaxies, corresponding to a detection rate of 81%. We compare the
gas content relative to blue and FIR luminosities of galaxies in compact groups
with respect to other samples in the literature, including various environments
and morphological types. We find that there is some hint of enhanced M(H2)/Lb
and M(dust)/Lb ratios in the galaxies from compact group with respect to our
control sample, especially for the most compact groups, suggesting that tidal
interactions can drive the gas component inwards, by removing its angular
momentum, and concentrating it in the dense central regions, where it is easily
detected. The molecular gas content in compact group galaxies is similar to
that in pairs and starburst samples. However, the total L(FIR) luminosity of
HCGs is quite similar to that of the control sample, and therefore the star
formation efficiency appears lower than in the control galaxies. However this
assumes that the FIR spatial distributions are similar in both samples which is
not the case at radio frequencies. Higher spatial resolution FIR data are
needed to make a valid comparison. Given their short dynamical friction
time-scale, it is possible that some of these systems are in the final stage
before merging, leading to ultra-luminous starburst phases. We also find for
all galaxy samples that the \htwo content (derived from CO luminosity and
normalised to blue luminosity) is strongly correlated to the L(FIR)luminosity,
while the total gas content H2+HI is not.
