Electric power systems are exposed to various contingencies. Network contingencies often contribute to over-loading of network branches, unsatisfactory voltages and also leading to voltage collapse. To maintain security against voltage collapse, it is desirable to estimate the effect of contingencies on the voltage stability. This paper presents a new approach using fuzzy logic to evaluate the degree of severity of the considered contingency and to eliminate masking effect in the technique. The proposed approach, in addition to real power loadings and bus voltage violations, voltage stability indices at the load buses are also used as the post-contingent quantities to evaluate the network contingency ranking. © 2007 CRL Publishing Ltd.