A method and an apparatus for providing control information for multi-carrier uplink transmission are disclosed. A wireless transmit/receive unit (WTRU) may set a happy bit for enhanced dedicated channel (E-DCH) transmissions on each uplink carrier considering aggregated transmission capability over all uplink carriers. The happy bit is set to “unhappy” if the WTRU is transmitting as much scheduled data as allowed by a current serving grant, the WTRU has enough power available to transmit at a higher rate, and total E-DCH buffer status (TEBS) requires more than a pre-configured period to be transmitted with a current effective data rate aggregated over all uplink carriers. The WTRU may send scheduling information including power headroom measured on the anchor uplink carrier and/or power headroom measured on the supplementary uplink carrier. For power headroom measurements, the WTRU may initiate a short-lived dedicated physical control channel loop on the supplementary carrier.