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This paper deals with spreading sequences selection for downlink and uplink Multi‐Carrier Code Division Multiple Access (MC‐CDMA) systems with the aim of minimizing the dynamic range of the transmitted multicarrier signal envelope and the multiple access interference. The crest factor of orthogonal and non‐orthogonal sequences are compared analytically and by simulation for downlink and uplink phase shift keying MC‐CDMA transmissions. Then, in order to minimize the multiple access interference produced by frequency selective channels, an optimized spreading sequence allocation procedure is presented. Finally, a selection of the spreading codes which jointly reduces the multiple access interference and the crest factor is proposed for downlink MC‐CDMA systems.