  The Gr\"uneisen ratio ($\Gamma$), i.e.\,the ratio of the linear thermal
expansivity to the specific heat at constant pressure, quantifies the degree of
anharmonicity of the potential governing the physical properties of a system.
While $\Gamma$ has been intensively explored in solid state physics, very
little is known about its behavior for gases. This is most likely due to the
difficulties posed to carry out both thermal expansion and specific heat
measurements in gases with high accuracy as a function of pressure and
temperature. Furthermore, to the best of our knowledge a comprehensive
discussion about the peculiarities of the Gr\"uneisen ratio is still lacking in
the literature. Here we report on a detailed and comprehensive overview of the
Gr\"uneisen ratio. Particular emphasis is placed on the analysis of $\Gamma$
for gases. The main findings of this work are: \emph{i)} for the Van der Waals
gas $\Gamma$ depends only on the co-volume $b$ due to interaction effects, it
is smaller than that for the ideal gas ($\Gamma$ = 2/3) and diverges upon
approaching the critical volume; \emph{ii)} for the Bose-Einstein condensation
of an ideal boson gas, assuming the transition as first-order $\Gamma$ diverges
upon approaching a critical volume, similarly to the Van der Waals gas;
\emph{iii)} for $^4$He at the superfluid transition $\Gamma$ shows a singular
behavior. Our results reveal that $\Gamma$ can be used as an appropriate
experimental tool to explore pressure-induced critical points.
