An ocean current is a continuous, directed flow of ocean water that can run for thousands of miles. Surface ocean currents (restricted to the upper 1000 ft or so) are largely wind driven, while deep ocean currents are driven by density and temperature gradients. Unlike tidal currents, which change direction and flow rate, ocean currents are relatively constant and flow in one direction only. In Alaska, the Aleutian passages have been identified as an area for potential development of ocean current energy extraction.
The type of turbine to be installed on an ocean current resource is similar to a tidal or in-river hydrokinetic one. As of late 2008, there are no commercial ocean current turbines in operation; however, several companies are exploring options for ocean-current energy extraction.