We have analyzed the total HI contents of 72 Hickson compact groups of galaxies ( HCGs ) and the detailed spatial distributions and kinematics of HI within a subset of 16 groups using the high angular resolution observations obtained with the VLA in order to investigate a possible evolutionary scenario for these densest systems in the present day galaxy hierarchy .
For the more homogeneous subsample of 48 groups , we found a mean HI deficiency of Def _ { HI } = 0.40 \pm 0.07 , which corresponds to 40 % of the expected HI for the optical luminosities and morphological types of the member galaxies .
The individual galaxies show larger degrees of deficiency than the groups globally , Def _ { HI } = 0.62 \pm 0.09 ( 24 % of the expected HI ) , due in most cases to efficient gas stripping from individual galaxies into the group environment visible in the VLA maps .
The degree of deficiency is found to be similar to the central galaxies of Virgo and Coma cluster , and Coma I group , in spite of the significantly different characteristics ( number of galaxies , velocity dispersion ) of these environments .
It does not seem plausible that a significant amount of extended HI has been missed by the observations .
Hence phase transformation of the atomic gas should explain the HI deficiency .
The groups richer in early type galaxies or more compact with larger velocity dispersions show a weak tendency to be more HI deficient .
The detection rate of HCGs at X-ray wavelengths is larger for HI deficient groups , although the hot gas distribution and hence its origin is only known for a few cases .
In the evolutionary scenario we propose , the amount of detected HI would decrease further with evolution , by continuous tidal stripping and/or heating .

The H _ { 2 } content also tends to be lower than expected for the galaxies in HI deficient groups , this may suggest that the HI stripping by frequent tidal interaction breaks the balance between the disruption of molecular clouds by star formation and the replenishment from the ambient HI .