For years, decades even - the pattern has been the same - nuclear runs first and then coal baseload followed by gas and then oil on the margin. This was the economic generation stack which reflected the generators earnings or spread (the difference between the power price and the fuel input price). 2009 has however seen an interesting reversal with gas plant increasingly running on a baseload basis and coal plant coming on line after gas. This is because although commodity prices have been eroded over the year, erosion of the gas price has been greater (a fall of around 33% in the S10 contract from July to December 09) than the erosion seen in the coal price (a fall of 5%). The net result is that the relative achievable clean dark and spark spreads have reversed with gas plant now achieving around a £6.00MWh premium on the clean dark spread. The reason lies partly with a healthy gas supply situation as well as global demand factors for coal. The situation doesn't appear to be a temporary blip either with the reversal set to continue into the new year.