In some multi-user radio systems the receiver is not allowed to transmit feedback information to the senders. In other applications the transmitters cannot receive feedback information sent by the receiver. For these cases a multiple access protocol is needed that maintains satisfactory performance in the absence of feedback. In this paper, such a protocol is introduced and an exact analysis of it is provided. The protocol, which uses an unconventional reservation mechanism, exploits the capability of interference rejection that Code Division Multiple Access (CDMA) provides.