  Chemical evolution models for the Galactic disk under an inside-out formation
scenario are presented for seven sets of stellar yields, all of them metal
dependent. In particular, the effects of yields from massive and
low-and-intermediate-mass stars on the C/O chemical history of the solar
neighborhood and on abundance gradients are discussed comparing the predictions
with abundance ratios from nearby HII regions, B-stars, dwarf stars, and the
Sun.
  In the solar vicinity, the increase of C/O with metallicity is due to massive
stars alone. Models with yields by Maeder (1992) or by Portinari, Chiosi, &
Bressan (1998) reproduce the observed C/O increase with metallicity, while
models assuming yields by Woosley & Weaver (1995) and Woosley, Langer, & Weaver
(1993) do not. Models based on yields by Maeder (1992) are in agreement with
the C/O gradient, while those based on yields by Portinari et al. (1998) or by
Woosley & Weaver (1995) and Woosley et al. (1993) are not. To match both, the
C/O enrichment history of the solar neighborhood and the C/O local gradient,
models call for: i) yields that take into account metal-dependent stellar
winds; and ii) for massive stars, a mass-loss rate with a metallicity
dependence not as simple as Z^{0.5}.
  C/O abundance ratios predicted with yields by Marigo, Bressan, & Chiosi
(1996, 1998) are higher than those with yields by Renzini & Voli (1981), which
in turn are higher than those with yields by the van den Hoek & Groenewegen
(1997).
