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Multicarrier (MC) modulation and code division multiple access (CDMA) schemes have seen much recent attention for the high capacities and flexibility they can provide. A potential difficulty with these systems is their sensitivity to the effects of imperfect frequency up/down conversion due to local oscillator phase noise and frequency offset. In this paper, we provide a general method to upper bound and/or approximate system performance in multitone direct-sequence spread spectrum (MT-DS-SS) signaling in the presence of imperfect synchronization. We model phase noise as a slow random processes with small variance. In particular, we assume coherent detection with binary phase-shift keying (BPSK) modulation and use a phase noise model based upon one for a practical phase-locked loop (PLL). Comparisons between simulations and analysis show excellent agreement, and also show that system degradation is dominated by the common phase noise, and that the intersubcarrier-same-user interference (IS-SUI) contribution is very small. The approach we employ provides an effective analytical/numerical method for performance evaluation for low target error probability values, on the order of 10-6 or lower. In addition, our method can also be easily applied to any multicarrier system with other frequency offset/phase noise models.