A new oil emulsion sprayed every 5 days during the fifty days from transplanting was found to be effective in four field experiments for two years in two environments (two in the north and two in the south of Italy), against aphid borne cucumber mosaic virus (CMV) and potato virus y (PVY) on tobacco. Oil was applied in mixture with imidacloprid at the rates of respectively 5,000 ml/ha and 90 ml/ha of a.i. and compared with imidacloprid alone and an untreated control. The incidence of viruses was evaluated by means of DOT-ELISA after 21, 40 and 68 days from transplanting, whereas the severity of symptoms was assessed by visual inspections, using an empirical scale from 0 (plants with no symptoms) to 5 (death plants) and the scores transformed according to Mc Kinney. No phytotoxic effects were found on tobacco plants because the oil used, Biolid, is a "narrow-ranged" oil, characterized by a prevailing presence of paraffin molecules with a reduced content of aromatic hydrocarbons, giving the product a lower phytotoxicity. Compared with both untreated control and imidacloprid alone, oil reduced the incidence of the viruses, in the first stages of plant growth, but the principal findings was that the severity of the symptoms in the plots treated with oil was always statistically lower than in the other plots. Oil sprayings gave better results with late and slower increase of the infection (northern Italy) than with early and faster increase of the infection (southern Italy).