A heat exchanger, preferably an oil cooler (1) for a motor vehicle, comprises stacked flat tubes (2, 3, 4), which have tube ends with apertures for admitting and discharging oil, which flows through the flat tubes (2, 3, 4) in their longitudinal direction. The apertures of adjacent flat tubes (2, 3, 4) are in fluid communication with one another in order to form flow passages, and spacings are left between the flat tubes for a medium, in particular a cooling medium, to pass through. The flat tubes are designed as extruded multi-channel tubes.