  We investigate global existence and optimal decay rates of a generic
non-conservative compressible two--fluid model with general constant
viscosities and capillary coefficients.The main novelty of this work is
three--fold: First, for any integer $\ell\geq3$, we show that the densities and
velocities converge to their corresponding equilibrium states at the $L^2$ rate
$(1+t)^{-\frac{3}{4}}$, and the $k$($\in [1, \ell]$)--order spatial derivatives
of them converge to zero at the $L^2$ rate $(1+t)^{-\frac{3}{4}-\frac{k}{2}}$,
which are the same as ones of the compressible Navier--Stokes system,
Navier--Stokes--Korteweg system and heat equation. Second, the linear
combination of the fraction densities
($\beta^+\alpha^+\rho^++\beta^-\alpha^-\rho^-$) converges to its corresponding
equilibrium state at the $L^2$ rate $(1+t)^{-\frac{3}{4}}$, and its $k$($\in
[1, \ell]$)--order spatial derivative converges to zero at the $L^2$ rate
$(1+t)^{-\frac{3}{4}-\frac{k}{2}}$, but the fraction densities
($\alpha^\pm\rho^\pm$) themselves converge to their corresponding equilibrium
states at the $L^2$ rate $(1+t)^{-\frac{1}{4}}$, and the $k$($\in [1,
\ell]$)--order spatial derivatives of them converge to zero at the $L^2$ rate
$(1+t)^{-\frac{1}{4}-\frac{k}{2}}$, which are slower than ones of their linear
combination ($\beta^+\alpha^+\rho^++\beta^-\alpha^-\rho^-$) and the densities.
We think that this phenomenon should owe to the special structure of the
system. Finally, for well--chosen initial data, we also prove the lower bounds
on the decay rates, which are the same as those of the upper decay rates.
Therefore, these decay rates are optimal for the compressible two--fluid model.
