At present, storage capacities of single tank and tank farm have been greatly increasing. This change poses a real challenge for the applicability of current design standards. This article focuses on the applicability of safety spacing between tanks, which is one of the most important parameters of tank farm safety design. Taking PHAST and FDS as main research tools, the consequences of representative accidental scenarios were evaluated for different sizes of oil tanks to study the safety performance change caused by the increase of capability. The research results show that, when current standards are used to design the safety spacing between tanks, the safety performance increases as the capability increases. Considering the high property density, it is suggested that a higher safety performance objective has to be chosen when designing the safety spacing for ultra-large oil tanks. © 2012 American Institute of Chemical Engineers Process Saf Prog, 2012.