  Time reversal symmetry is a fundamental property of many quantum mechanical
systems. The relation between statistical physics and time reversal is subtle
and not all statistical theories conserve this particular symmetry, most
notably hydrodynamic equations and kinetic equations such as the Boltzmann
equation. In this article it is shown analytically that quantum kinetic
generalizations of the Boltzmann equation that are derived using the
nonequilibrium Green functions formalism as well as all approximations that
stem from $\Phi$-derivable selfenergies are time reversal invariant.
