  Analytic results are presented for preheating in both flat and open models of
chaotic inflation, for the case of massless inflaton decay into further
inflaton quanta. It is demonstrated that preheating in both these cases closely
resembles that in Minkowski spacetime. Furthermore, quantitative differences
between preheating in spatially-flat and open models of inflation remain of
order $10^{-2}$ for the chaotic inflation initial conditions considered here.
