The difference between the market price of electricity and the market price of the fuel (gas) used to generate it, adjusted for generation efficiency/heat rate. The spark spread can be expressed per megawatt hour (for example £/MWh) or other applicable energy units. A clean spark spread takes account of the CO≤ emissions cost. When the fuel is coal, the spread is often referred to as a ''dark spread''. The spark spread does not consider the cost of production. It helps utility companies determine their profits; if it is negative, the utility company loses money, and if it is positive, the utility company makes money.