Linear stability analysis of a liquid–vapor interface under adverse gravitational field and velocity streaming is considered. The liquid is assumed viscous, incompressible, and motionless over a vapor layer with a uniform horizontal velocity. It is shown that while the coupled viscosity‐phase change mechanism of former studies adds considerably to the stability of the Rayleigh–Taylor problem, it has a deleterious effect on the Kelvin–Helmholtz mode of stability. ©1995 American Institute of Physics.