Techniques for acknowledging data transmissions in a multi-carrier wireless communication network are disclosed. In some aspects, a user equipment (UE) receives a data transmission on at least one component carrier (CC) in a plurality of configured CCs. The UE determines acknowledgement/negative acknowledgement (ACK/NACK) information for the data transmission and determines an uplink channel for sending the ACK/NACK information. When the ACK/NACK information is sent on a physical uplink control channel (PUCCH), the UE may perform power control based on which CCs in the plurality of configured CCs data is received. When the ACK/NACK information is sent on a physical uplink shared channel (PUSCH), the UE may determine a number of resource elements based on its CC configuration.