This paper analyzes the role of fuel flexibility in the West European power generation sector. Fuel flexibility is recognized to have two important features. It improves the power sector's ability to respond to fuel supply interruptions, and it permits short-run price-induced interfuel competition. The security of supply issue is examined by assessing the ability of the West European power sector to respond to an interruption in gas imports. This ability is found to be high. Especially the use of oil in dual- and multi-fired plants provides a significant buffer against a potential gas supply cut. In an attempt to measure the degree of price-induced interfuel substitution in West European power generation two flexible cost functions are employed; the Translog and the Generalized Leontief. The cross-price elasticities of fossil fuel demand generated by these indicate notable short-run interfuel substitution in Western Europe, in particular between oil and gas. Since emerging competitive electricity and gas markets normally induce utilities to reduce fuel costs through improved fuel contracting, short-run interfuel substitution is likely to remain significant also in the future. This has important implications for European energy markets and policies.