Why are additives not added by the oil suppliers at the refinery itself?
The answer to this question is largely a commercial one. Oil companies are supplying a residual or a waste product at a relatively fair price. Blending of an additive into bulk quantities of fuel oil is both complicated and a costly procedure. Besides, the fuel oil could be destined for a wide variety of uses some of which require additive treatment and some of which do not. There is also the possibility that in certain industrial processes the compounds in the additive may actually do harm to the product that is being manufactured.
