For the purpose of enhancing the seismic reliability of structures, external energy dissipation systems may be advantageously used. In this paper, the reliabilities of a spherical storage tank in original and updated states are assessed by means of simulation. The effect of the energy dissipation system is numerically evaluated by performing a set of nonlinear dynamic analyses on a spherical tank based on a detailed model that takes the fluid–structure interaction into account. To obtain robust estimators of the reliability, an ensemble including acceleration records with markedly different characteristics is used in the simulation study. The full reliability analysis shows that, for a typical spherical container widely used in the petrochemical industries, a reduction of the limit state probability in the order of 85% may be expected by introducing additional energy dissipation systems.