We analyze evolution of live disk-halo systems with gas fractions, fgas<=8% of the disk mass, for 5 Gyr. Specifically, we have addressed the issue of angular momentum (J) transfer from the gas to the stellar bar and its effect on the bar. We find that the bar weakening, reported in the literature, is not related to the gas, but is caused by the vertical buckling instability in the gas-poor disks and by a steep stellar heating by the central mass concentration (CMC) in the gas-rich disks. However, the gas has a profound effect on the onset of the buckling: larger fgas brings it forth due to the more massive CMCs. The former process leads to the well-known formation of the boxy/peanut-shaped bulges, while the latter results in the formation of more elliptical bulges, for larger fgas. The subsequent secular bar evolution differs: the gas-poor models exhibit a growing bar while gas-rich models show a declining bar whose vertical swelling is driven by a resonance heating. The borderline between the gas-poor and gas-rich models is model-dependent and will be affected by processes such as star formation and stellar feedback. The overall effect of the gas on the bar is not in a direct J transfer to the stars, but in the loss of J by the gas and the gas influx to the center. A more massive CMC damps the bar buckling and depopulates orbits responsible for the appearance of boxy/peanut-shaped bulges. The combined action of resonant and nonresonant processes in gas-poor and gas-rich disks leads to a converging evolution in the vertical extent of the bar and its stellar dispersion velocities, and to a diverging evolution in the bulge properties.