Drift-flux models can be used to describe two-phase-flow systems when explicit representation of the relative phase motion is not required. In these models, relative phase velocity is described by flow-regime-dependent, semiempirical models. Numerical stability of the mixture drift-flux equations is examined for different semi-implicit time discretization schemes. Representative flow-regime-dependent drift-flux correlations are considered, and analytic stability limits are derived based on these correlations. The analytic stability limits are verified by numerical experiments run in the vicinity of the predicted stable boundaries. It is shown that the stability limits are strong functions of the time-level specification and functional form chosen for the relative phase velocity. It is also shown that the mixture Courant limit normally associated with these methods is insufficient for ensuring a stable numerical scheme.