To an aniline of formula (Ⅰ) is used as a marker of the mineral oil, the aniline is detected in the mineral O'Neill. Wherein R, R ¹ and R ² are independently hydrogen atom, optionally substituted or not substituted on being unsubstituted functional group interrupted by one to three oxygen atoms, or aminoalkyl, or substituted phenyl, or R ¹ and R ² are each or a 5-or 6-membered cyclic saturated heterocyclic radical which may further contain other hetero atoms together with the nitrogen atom, R ¹ is or substituted hydrogen is optionally substituted and the unsubstituted or substituted amino, R ³ and R ⁷ are different from each independently hydrogen, unsubstituted or alkyl, alkenyl which is unsubstituted, cyano, nitro, formyl, optionally substituted C ₂ -C ₄ - alkanoyl, formyl, amino, optionally substituted C ₂ -C ₄ - alkanoylamino, benzoylamino, or, optionally substituted with R ^2, or one or alkylene substituted to trisubstituted by an alkyl group or unsubstituted or phenyl-substituted alkenylene, and, R ⁴ is Hydrogen, optionally substituted alkyl, alkenyl, cyano, alkenyl, nitro, unsubstituted, R ⁵ and R ⁶ are each hydrogen, a substituted or non-alkyl, alkenyl, unsubstituted, optionally substituted phenyl, nitro, acylamino, substituted or unsubstituted hydroxyl, substituted or unsubstituted sulfamoyl, alkyl-, alkenyl-or arylsulfonyl, acyl or substituted or a carboxylic acid which is unsubstituted, radical R ^3, R ⁵ or R, at least one of the ^seven is It is hydrogen.