Abstract: To investigate the differences in potential response and associated hazard mechanisms of external floating roof oil tanks under various lightning conditions, this study conducted systematic comparative experiments at the China Meteorological Administration's Lightning Field Experiment Base using artificially triggered lightning. Two representative lightning scenarios—direct strikes and induced lightning (ground potential rise, GPR)—were examined. The experiments involved synchronous acquisition of potential difference waveforms between the tank wall and the floating roof, along with lightning current parameters, to analyze their temporal characteristics and electromagnetic coupling behavior. Results show that under direct lightning strikes, the potential difference can reach a peak of 12.77 kV with a duration up to 0.1 ms. When the return stroke current exceeds 20 kA, double-peak waveforms and prolonged potential duration are likely to occur, significantly increasing the risk of breakdown across the oil-gas gap. In contrast, under GPR conditions induced by nearby lightning, the potential difference is relatively lower (-3.4 kV~1.23 kV), but the rise steepness is extremely high—up to two orders of magnitude greater under ungrounded conditions than grounded ones. The waveform polarity is also strongly influenced by the strike location and grounding status. The study highlights that the response mechanisms of oil tanks differ markedly between lightning types, necessitating differentiated protection strategies: for direct strikes, emphasis should be placed on maintaining equipotential bonding and controlling return stroke current; for GPR scenarios, grounding system design and suppression of induced coupling paths should be prioritized. These findings provide empirical evidence and technical guidance for lightning protection engineering of oil storage tanks.