Abstract: An additive concentrate has at least one nitrogen-containing deposit control additive, a solvent, and at least one tagging material. The tagging material has a number average molecular weight of at least 15,000 and a weight average to number average molecular weight ratio of less than 1.5. The tagging material has a molecular weight distribution that is sufficiently different from the molecular weight distribution of the deposit control additive so as to be distinguishable from the deposit control additive. The amount of each tagging material is less than 1 weight % of the additive concentrate.

Abstract: Gasolines are identified from one another by adding to at least one of the gasolines at least one tagging material which is unique to that gasoline. Each unique tagging material has a number average molecular weight of at least 15,000 and is present at a level of less than 1.0 ppm of the gasoline. In addition, each unique tagging material must be soluble in the composition to be tagged, must not vaporize or thermally degrade at temperatures below about 120.degree. C., must not contribute to degradation of hydrocarbon filterability: and must not contribute to engine harm. A sample of the gasoline is vaporized to form a liquid residue; and the liquid residue is analyzed for the presence of the tagging material in the residue to thereby identify the particular gasoline.