The oil regeneration process consists of connecting the regeneration unit into the oil circuit of the transformer and then pumping the oil through various sieves, filters and heaters to remove impurities and dry the oil. In order to ensure this is economically viable it is essential to properly understand the effect of the regeneration on the transformer oil condition and the subsequent rates of deterioration following the proposed intervention which is made more difficult due to the loss of historical oil data held in the untreated oil