An essential aspect of modern power system security assessment is the consideration of any contingencies which may arise due, for example, to planned or unplanned outages of lines, and which may cause system overloads or abnormal system voltages. Several methods have been developed during the last few years to address this problem and within the National Grid Company, the /spl Delta/P/sup 2/X outage ranking process has been used in the past. However, this /spl Delta/P/sup 2/X outage ranking method may not identify those critical outages associated with relatively low /spl Delta/P/sup 2/X changes. The paper reports on investigations carried out to determine which simplified methods would ensure that all voltage-based severe outages were identified.