A method for circular use of industrial oil, said method comprising reconditioning of a used industrial oil, said reconditioning comprising the steps of: - adding a liquid separation booster to a used industrial oil, wherein said separation booster is designed to attract impurities in the used oil and to be passive onto, i.e. not attracting, at least one specific functional additive in the oil, wherein said liquid separation booster is substantially insoluble in the oil because of its polars properties, forming a two phase mixture upon mixing thus forming colloids consisting of small droplets of the liquid separation booster, which through chemical interactions absorb impurities being contaminating solids or dissolved impurities, whereby said separation booster attracts impurities in the oil during mixing of oil and separation booster and wherein the separation booster has a sufficiently big difference in polarity compared to polarity of the at least one specific functional additive in the industrial oil such that the at least one specific functional additive is not soluble in the separation booster; - separating out the separation booster with attracted impurities from the used industrial oil while leaving the at least one specific additive in the oil; - analyzing the used oil to identify depletion of certain functional additives in the used oil; and - adding functional additives to the used oil, wherein the step of adding functional additives to the used oil comprises adding those functional additives which have been identified as depleted and in an amount corresponding to the identified depletion, wherein the functional additives added to the used oil is one or more of oxidation inhibitors, corrosion inhibitors, rust inhibitors, anti-wear agents, extreme pressure agents, friction modifiers, detergents, dispersants, pour point depressants, viscosity index improvers and foam inhibitors. - adding a liquid separation booster to a used industrial oil, wherein said separation booster is designed to attract impurities in the used oil and to be passive onto, i.e. not attracting, at least one specific functional additive in the oil, wherein said liquid separation booster is substantially insoluble in the oil because of its polars properties, forming a two phase mixture upon mixing thus forming colloids consisting of small droplets of the liquid separation booster, which through chemical interactions absorb impurities being contaminating solids or dissolved impurities, whereby said separation booster attracts impurities in the oil during mixing of oil and separation booster and wherein the separation booster has a sufficiently big difference in polarity compared to polarity of the at least one specific functional additive in the industrial oil such that the at least one specific functional additive is not soluble in the separation booster; - separating out the separation booster with attracted impurities from the used industrial oil while leaving the at least one specific additive in the oil; - analyzing the used oil to identify depletion of certain functional additives in the used oil; and - adding functional additives to the used oil, wherein the step of adding functional additives to the used oil comprises adding those functional additives which have been identified as depleted and in an amount corresponding to the identified depletion, wherein the functional additives added to the used oil is one or more of oxidation inhibitors, corrosion inhibitors, rust inhibitors, anti-wear agents, extreme pressure agents, friction modifiers, detergents, dispersants, pour point depressants, viscosity index improvers and foam inhibitors.