An adjustable camshaft may include an outer shaft that is hollow and an inner shaft received in the outer shaft and rotatable in the outer shaft. The inner shaft may include a cavity into which oil can be applied. At least a first radial opening may be configured in the outer shaft and at least a second radial opening may be configured in the inner shaft. Thus oil can flow between the cavity and an outside of the outer shaft during overlap of the first radial opening and the second radial opening. The first radial opening on an inside of the outer shaft may have a greater cross-section than on the outside of the outer shaft.