where Pit, J = 1, 2, 3 are the prices 1 of each fuel, C t is total fossil fuel demand at time t, and the Zkt are a set of n exogenous variables of interest. The Z variables include such factors as GDP, consumption of nuclear energy, consumption of hydroelectricity, and in some cases dummy variables representing various one-off shocks such as strikes and events due to government policy, such as investment pro- grammes in power stations, as shown in Table 3.