Heating oil and natural gas are indeed substitutes in electricity generation and certain industrial uses, which induces fuel switching and price correlation in the short or medium terms. In electricity generation for instance, gas-fired plants exhibit a very high sensitivity to fuel prices as a two-fold increase in the fuel cost can augment the cost of generating electricity by over a third (IEA/NEA, 2010). On the contrary, for nuclear power plants the fuel price risk is generally much lower than for fossil-fuelled plants, since fuel costs are a small share of total cost, indeed even a doubling of the cost of uranium would only increase the share of fuel costs from 10% to about 20%, implying an increase of about 10% in the total cost of electricity produced by a nuclear plant. This translates into stable costs over the lifetime of a plant and, depending on market structure, potentially into stable electricity prices. In 2008 the ratio of spot to total deliveries in the EU-27 was 2.8% (Euratom Annual report, 2008).