Methods and apparatuses are provided for uplink MIMO transmissions in a wireless communication system. In some particular aspects, an E-TFC selection process for selecting a transport format combination for an uplink MIMO transmission may take certain steps in the case that a UE is power- or buffer-limited. For example, in a rank 2 transmission, non-scheduled data is allocated only to the primary stream. If the allocated non-scheduled data is less than the determined primary stream transport block size, scheduled data is allocated to the primary stream in an amount not to exceed the determined primary stream TBS. Finally, scheduled data is allocated to the secondary stream in an amount not to exceed the determined secondary stream TBS.