An ocean current that is the product of a balance between pressure-gradient forces and the Coriolis effect. This produces a current flow along the pressure gradient. Such a current does not flow directly from a region of higher pressure to one of lower pressure (i.e. ‘down the slope’ of the sea surface) but flows parallel to the gradient. All the major currents in the oceans, such as the Gulf Stream, are very nearly true geostrophic currents. The Gulf Stream, for example, can be likened to a river that does not run down a hill but around the hill.