The aniline point of an oil is defined as the minimum temperature at which equal volumes of aniline (C6H5NH2) and lubricant oil are miscible, i.e. form a single phase upon mixing.
The lower the aniline point, the greater is the content of aromatic compounds in the oil.
The aniline point serves as a reasonable proxy for aromaticity of oils consisting mostly of saturated hydrocarbons (i.e. alkanes, paraffins) or unsaturated compounds (mostly aromatics).
[2] Equal volumes of aniline and oil are stirred continuously in a test tube and heated until the two merge into a homogeneous solution.
The temperature at which the two phases separate out is recorded as aniline point.