Drift-flux models can be used to describe two-phase-flow systems when expli
cit representation of the relative phase motion is nor required In these mo
dels, relative phase velocity is described by flow-regime-dependent, semiem
pirical models. Numerical stability of the mixture drift-flux equations is
examined for different semi-implicit time discretization schemes. Represent
ative flow-regime-dependent drift-flux correlations are considered, and ana
lytic stability limits are derived based on these correlations. The analyti
c stability limits are verified by numerical experiments run in the vicinit
y of the predicted stable boundaries. It is shown that the stability limits
are strong functions of the time-level specification and functional form c
hosen for the relative phase velocity. It is also shown that the mixture Co
urant limit normally associated with these methods is insufficient for ensu
ring a stable numerical scheme.