By analyzing the existing data of S0 galaxies for which the kinematics of the ionized gas and stellar components were measured along (at least) the major axis, Pizzella et al. (2004) found a counter-rotating (or a kinematically decoupled) gaseous component in 17/53 galaxies. This fraction corresponds to 32%-11+19 (at the 95% confidence level) and it is consistent with previous statistics by Bertola et al. (1992, 35%), Kuijken et al. (1996, (24 ± 8)%), and Kannappan & Fabricant (2001, 24%-6+8). These findings favor a scenario in which acquisition events in S0 galaxies are not limited to few peculiar objects but they are a widespread phenomenon (Bertola et al. 1992), as it is for ellipticals (Bertola et al. 1988). The recent results by Davis et al. (2011) based on integral-field spectroscopy and radio observations support this scenario too. They found that the gas in (36 ± 5)% (40/111) of their sample of fast-rotating early-type galaxies is kinematically misaligned with respect to the stars. In addition, the ionized, molecular, and atomic gas in all the detected galaxies are always kinematically aligned, even when they are kinematically misaligned from the stars. This implies that all these phases of the interstellar medium share a common origin and underlines the role of external acquisition.
In contrast to the prevalence of counter-rotating gas in S0 galaxies, (Kuijken et al. 1996) estimated than < 10% (at the 95% confidence level) of S0 galaxies host a significant fraction (> 5%) of counter-rotating stars.
Pizzella et al. (2004) addressed the frequency of counter-rotation in spiral galaxies from a sample of 50 S0/a-Scd galaxies, for which the major-axis kinematics of the ionized gas and stars were obtained with the same spatial and spectral resolution, and measured with the same analysis techniques. It turns out that < 12% and < 8% (at the 95% confidence level) of the sample galaxies host a counter-rotating gaseous and stellar disk, respectively. For comparison, Kannappan & Fabricant (2001) set an upper limit of 8% on the fraction of spirals hosting counter-rotating gas by analyzing a sample of 38 Sa-Sbc galaxies.