  The Oxygen abundance in the solar photosphere, and consequently the solar
metallicity itself, is still a controversial issue with far-reaching
implications in many areas of Astrophysics. This paper presents a new
determination obtained by fitting the forbidden OI line at 6300 A with an
observational 3D model. The approach presented here is novel because previous
determinations were based either on 1D empirical stratifications or on 3D
theoretical models. The resulting best-fit abundances are lg E(O)=8.90 and lg
E(Ni)=6.15. Nevertheless, introducing minor tweaks in the model and the
procedure, it is possible to retrieve very different values, even down to lg
E(O)=8.70. This extreme sensitivity of the abundance to possible systematic
effects is not something specific to this particular work but probably reflects
the real uncertainty inherent to all abundance determinations based on a
prescribed model atmosphere.
