  We explore the growth and the evolution of the bar instability in
stellar-gaseous disks embedded in a suitable dark matter halo evolving in a
fully consistent cosmological framework. The aim of this paper is to point out
the impact of different gas fractions on the bar formation, inside disks of
different disk-to-halo mass ratio, and the role of the cosmological framework.
We perform cosmological simulations with the same disk-to-halo mass ratios as
in a previous work where the gas was not taken into account. We compare results
of the new simulations with the previous ones to investigate the effect of the
gas by analysing the morphology of the stellar and gaseous components, the
stellar bar strength and the behaviour of its pattern speed. In our
cosmological simulations, inside dark-matter dominated disks, a stellar bar,
lasting 10 Gyr, is still living at z=0 even if the gaseous fraction exceeds
half of the disk mass. However, in the most massive disks we find a threshold
value (0.2) of the gas fraction able to destroy the bar. The stellar bar
strength is enhanced by the gas and in the more massive disks higher gas
fractions increase the bar pattern speed.
