Based on recent insights from the field of risk analysis, this paper examines some of the difficulties encountered in attempts to characterise the environmental effects of energy options as monetary ＇externalities＇, More than 20 different dimensions of environmental appraisal are identified and discussed in relation to the historic literature on risk assessment and a number of recent influential environmental valuation studies, A survey is conducted of the results obtained over more than a decade for the external environmental costs of electricity supply options, Theoretical and methodological criticisms are lent support by the finding that environmental valuation results vary over a very wide range of values, yielding a variety of rank orderings for the different generating options, In addition, the values derived for energy externalities are found to be vulnerable to the possible influence of a ＇price imperative＇. The paper concludes by pointing to approaches to the social appraisal of generating technologies which offer greater transparency, rigour and accessibility in addressing plural and intrinsically subjective value judgements concerning the different forms and dimensions of environmental effects.