  We compare magnetotransport measurements under pressure on the organic
superconductor $\kappa$-(BEDT-TTF)$_{2}$Cu(SCN)$_{2}$ with different
pressure-media and discover that the results are pressure media dependent. This
pressure-medium dependence is thought to originate from the difference in
thermal contraction between the very soft and highly anisotropic sample and the
isotropically contracting, but solid pressure medium, thus resulting in
non-hydrostatic pressure on the sample. However, comparison of pressure
measurements with different media reveals a pressure-medium independent
correlation between the superconducting transition temperature, T$_{\rm c}$,
and the size of the quasi 2-dimensional Fermi surface pocket and thus the quasi
2-dimensional carrier density in $\kappa$-(BEDT-TTF)$_{2}$Cu(SCN)$_{2}$. The
observed pressure-induced increase in the quasi 2-dimensional carrier density
can be interpreted as a transfer of carriers from quasi 1-dimensional Fermi
surface sections, reminiscent of a mechanism in cuprate superconductors, where
pressure is known to transfer carriers from the insulating charge reservoir
layers into the conducting cuprate sheets.
