  Transit surveys combined with Doppler data have revealed a class of gas giant
planets that are massive and highly enriched in heavy elements (e.g.,
HD149026b, GJ436b, and HAT-P-20b). It is tempting to consider these planets as
validation of core accretion plus gas capture because it is often assumed that
disk instability planets should be of nebular composition. We show in this
paper, to the contrary, that gas giants that form by disk instability can have
a variety of heavy element compositions, ranging from sub- to super-nebular
values. High levels of enrichment can be achieved through one or multiple
mechanisms, including enrichment at birth, planetesimal capture, and
differentiation plus tidal stripping. As a result, the metallicity of an
individual gas giant cannot be used to discriminate between gas giant formation
modes.
