Simultaneous LNG bunkering operations involve the concurrent execution of on/off loading and LNG bunkering. While this approach is economically advantageous due to reduced bunkering time, it also increases operational hazards. Consequently, the need for standardized safety regulations for bunkering simultaneous operations has become increasingly urgent. In this study, the safety of such operations under ocean wave conditions is investigated through numerical analysis for both the receiving and bunkering ships. The analysis considers both ship-to-ship (STS) and ship-to-wall (STW) configurations, examining how motion responses are affected by environmental conditions. The results confirm that both vessels are significantly influenced by wave reflections from the quay wall. Additionally, the bunkering ship is further affected by the presence of the receiving ship. When irregular waves act on the side-by-side moored vessels at the quay wall, the motion of the relatively smaller bunker