  In this paper we discuss the incompressible limit for multicomponent fluids
in the isothermal ideal case. Both a direct limit-passage in the equation of
state and the low Mach-number limit in rescaled PDEs are investigated. Using
the relative energy inequality, we obtain convergence results for the densities
and the velocity-field under the condition that the incompressible model
possesses a sufficiently smooth solution, which is granted at least for a short
time. Moreover, in comparison to single-component flows, uniform estimates and
the convergence of the pressure are needed in the multicomponent case because
the incompressible velocity field is not divergence-free. We show that certain
constellations of the mobility tensor allow to control gradients of the
entropic variables and yield the convergence of the pressure in L1.
