  We use the relationships between galactic HI mass and B-band luminosity
determined by Rao & Briggs to recalculate the mass density of neutral gas at
the present epoch based on more recent measures of the galaxy luminosity
function than were available to those authors. We find $\Omega_{gas}(z=0)
\simeq 5 \times 10^{-4}$ in good agreement with the original Rao & Briggs
value, suggesting that this quantity is now reasonably secure. We then show
that, if the scaling between H I mass and B-band luminosity has remained
approximately constant since $z = 1$, the evolution of the luminosity function
found by the Canada-France redshift survey translates to an increase of
$\Omega_{gas}$ by a factor of $\approx 3$ at $z = 0.5 - 1$ . A similar value is
obtained quite independently from consideration of the luminosity function of
Mg II absorbers at $z = 0.65$. By combining these new estimates with data from
damped \lya systems at higher redshift, it is possible to assemble a rough
sketch of the evolution of $\Omega_{gas}$ over the last 90% of the age of the
universe. The consumption of H I gas with time is in broad agreement with
models of chemical evolution which include the effects of dust, although more
extensive samples of damped \lya systems at low and intermediate redshift are
required for a quantitative assessment of the dust bias.
