A survey of relevant numerical, laboratory, and observational studies, combined with our own laboratory experiments, suggests that the surface outflow from a strait generally forms a gyre in the adjacent sea if the exit corner is sharp. The gyre grows from an initial ''separation bubble'' of radius u/f, where u is the current speed and f the Coriolis frequency. The criterion for the maintenance of a coastal jet along a curved coast, instead of separation and gyre formation, seems to be that the Rossby number u(f Rw)-1<1, with Rw the radius of curvature of the exit corner, so that the coriolis force can hold the current to the coast. This synthesis disregards factors such as the variation of u across the current but, applied to the flow through the Strait of Gibraltar into the Alboran Sea, suggests that a gyre should always form as the exit corner is sharp. We suggest, though, that the relevant curvature is that where the interface between the two layers intersects the seafloor rather than where the sea surface meets the coast. If this is the case, supercritical flow or some subcritical flows at the eastern end of the Strait should still always lead to gyre formation, but the observed replacement of the gyre by a coastal jet along the Moroccan coast could be related to subcritical flow that is reduced below its normal value by a barotropic fluctuation or by changes in the interface depth in the Mediterranean. ¿ American Geophysical Union 1989