  We model the interaction of the supernova SN 1995G with a dense circumstellar
(CS) gas in a thin shell approximation. A model fit of the observed bolometric
light curve combined with data on the supernova expansion velocity provides an
estimate of the density of the CS shell, its mass ($\approx 1 M_{\odot}$), and
age ($\approx 8$ years). It is shown that the derived CS gas density does not
depend on the assumed mass of the supernova ejecta. This results from the high
CS density, which ensures that the forward shock wave is essentially radiative.
The derived CS density is consistent with the H$\alpha$ luminosity and with the
presence of the apparent effect of Thomson scattering in the red wing of this
line. The mass of the CS envelope together with its expansion velocity
indicates that the CS envelope was ejected as a result of violent energy
release ($\sim 6\times10^{48}$ erg) eight years before the supernova outburst.
