In this paper we present the results of a systematic study of resistive states cycling dispersion in HfOx Resistive Random Access Memory (RRAM). A wide set of experimental data is collected on several RRAM devices in different operating conditions. A compact model is exploited lo link the device electrical response to its physical characteristics, delivering a clear physical picture of cycling dispersion and of its sensitivity to operating conditions. The implications of operating voltage, current compliance, and temperature on the device reliability are clarified. Particularly, the dispersion of both RHRS and RLRS is much worsened at low current compliance, which reduces the worst-case read window establishing a trade-off between device reliability and power consumption.