The trade was a winter 2005 deal at £2.21 a megawatt hour (MWh), in 15 MW of power versus 25,000 therms of natural gas and 25,000 EU emissions allowances (EUAs).

The spark spread is the spread between the value of electricity and the fuel used to generate that electricity. Power generators commonly engineer over-the-counter forward trades to lock in spark spreads, in order to protect against gas price volatility.

But now, generators must also factor in the cost of the CO₂ emissions