A method and network node for adaptation of contention windows in a multicarrier wireless communication system implementing a listen-before-talk protocol are disclosed. According to one aspect, a method includes determining at least one component carrier (CC), of multiple CCs to serve as a backoff channel. The method further includes performing a listen-before-talk procedure on the at least one CC serving as a backoff channel. The listen-before-talk procedure includes sensing for each backoff channel whether a clear channel exists during a backoff period drawn from a contention window (CW). The LBT procedure also includes deferring transmitting on a CC for which the sensing does not indicate that a clear channel exists. The LBT procedure also includes transmitting on a CC for which the sensing indicates a clear channel exists. The method also includes determining a size of the CW based on at least one transmission feedback value.