Abstract: A method and an apparatus for measured injection of additives into oil products and the like, in particular aims at the filling of fuel in tank farms for transport by tank trucks. Each batch of fuel shall have a pre-set proportion of additive. After each terminated filling and successively at a number larger than one, there is recorded a signal (S6) which represents discrepancies between actually supplied amount of additive and the amount which corresponds to the pre-set proportion. From the first signal (S6) there is calculated a further signal (S7) which represents discrepancies throughout said number of fillings and this further signal serves as a reference or correction value during the subsequent filling operation. A particular supply conduit (10) for fuel is adapted to give a through flow of fuel in order to remove remaining amounts of additive from the measuring system itself.