  We study supersymmetric scenarios in which the gluino is the next-to-lightest
supersymmetric particle (NLSP), with a mass sufficiently close to that of the
lightest supersymmetric particle (LSP) that gluino coannihilation becomes
important. One of these scenarios is the MSSM with soft supersymmetry-breaking
squark and slepton masses that are universal at an input GUT renormalization
scale, but with non-universal gaugino masses. The other scenario is an
extension of the MSSM to include vector-like supermultiplets. In both
scenarios, we identify the regions of parameter space where gluino
coannihilation is important, and discuss their relations to other regions of
parameter space where other mechanisms bring the dark matter density into the
range allowed by cosmology. In the case of the non-universal MSSM scenario, we
find that the allowed range of parameter space is constrained by the
requirement of electroweak symmetry breaking, the avoidance of a charged LSP
and the measured mass of the Higgs boson, in particular, as well as the
appearance of other dark matter (co)annihilation processes. Nevertheless, LSP
masses $m_\chi \lesssim 8$~TeV with the correct dark matter density are quite
possible. In the case of pure gravity mediation with additional vector-like
supermultiplets, changes to the anomaly-mediated gluino mass and the threshold
effects associated with these states can make the gluino almost degenerate with
the LSP, and we find a similar upper bound.
