The collaborative coding multiple-access (CCMA) technique potentially permits efficient simultaneous transmission by several users sharing a common channel, without subdivision in time or frequency. The capacity of a T-user binary adder multiple-access channel is calculated for additive white Gaussian noise (AWGN) conditions. The capacity in bits/ channel use for different numbers of users is derived by simulation for the baseband antipodal and bandpass on-off keying systems with coherent and noncoherent combining. It is shown that in principle T-user CCMA permits higher transmission rates than time-division multiple-access (TDMA) employing the same signal alphabet.