  We present the analysis of a survey of atomic and molecular gas in
interacting and merging galaxies (Horellou & Booth 1997). The sample is
optically selected and contains all interacting galaxies (~ 60 systems) in a
well-defined region of the Southern sky (Bergvall 1981). In order to take into
account the upper limits due to non-detections, we have carried out a survival
analysis. The results are compared with the ones obtained when ignoring the
non-detections. We have found evidence for a lower atomic gas content per unit
area in interacting galaxies compared to isolated ones. Except for a few
systems with high far-infrared luminosity and correspondingly high CO fluxes,
the interacting galaxies are not unusually CO-bright. The observed
HI-deficiency is therefore not due to a conversion from HI into H2. Atomic gas
from the outer part of the galaxies may have been swept by tidal interaction,
or the optical extent of the galaxies may have increased due to the tidal
interaction. The interacting galaxies seem to be more efficient at transforming
their molecular gas into stars, as indicated by their higher LFIR/M(H2) ratio.
We found no correlation between molecular gas fraction and degree of
morphological distortion.
