The spark spread is the theoretical gross margin of a gas-fired power plant from selling a unit of electricity, having bought the fuel required to produce this unit of electricity. All other costs (operation and maintenance, capital and other financial costs) must be covered from the spark spread. The term was first coined by Tony West's trading team on the trading floor of National Power Ltd in Swindon, UK during the late 1990s and quickly came into common usage as other traders realised the trading and hedging opportunities.
The terms dark spread, quark spread and bark spread[1][2] refer to the similarly defined differences ("spreads") between cash streams for coal-fired power plants, nuclear power plants and bio-mass power plants, respectively. These indicators of power plant economics are useful for trading energy markets. For operating or investment decisions published "spread" data are not applicable. Local market conditions, actual plant efficiencies and other plant costs have to be considered. A higher dark spread is more economically beneficial to the owner of the generator; an IPP with a dark spread of €15/MWh will be more profitable than a competitor with a dark spread of only €10/MWh.
Further definition of clean spread indicators include the price of carbon dioxide emission allowances (see: Emission trading).