A diesel composition, which comprises a base diesel and an additive composition, characterized in that said base diesel comprises biodiesel, and said additive composition comprises component (a) and component (b), wherein said component (a) is a substituted p-phenylene diamine, and said component (b) is one or more polyamines or derivatives thereof, wherein the polyamine is a polyether diamine of formula: wherein x1 is an integer from 1 to 10, R 4 is H or a hydrocarbyl having 1 to 30 carbon atoms, and R 5 is H or methyl: or a polyene polyamine of the structural formula: H 2 N[(CH 2) x2 NH] y1 R 6 wherein x2 is an integer from 2 to 4, y1 is an integer from 1 to 8, and R 6 is H or a hydrocarbyl having 1 to 30 carbon atoms, and/or a condensate of said polyene polyamine with ethylene oxide and/or propylene oxide; or an imidazoline-type polyamine of the formula; wherein y2 is an integer from 0 to 5, and R 7 is a hydrocarbyl having 1 to 24 carbon atoms; or a piperazine-type polyamine being N-(2-aminoethyl)piperazine or N,N'-di-(aminoethyl)piperazine; or a piperidine-type polyamine: or a tertiary amine containing polyamine of the formula (A 4), (A 5) or: wherein R 9 and R 10 are hydrocarbyls having 1 to 24 carbon atoms, and x4 is an integer from 0 to 10; or wherein x5 is an integer from 1 to 10; or wherein R 11 is a hydrocarbyl having 1 to 24 carbon atoms, and x6 is an integer from 1 to 10, and preferably an integer from 2 to 6; wherein said derivatives of polyamines are the reaction products of the ammonolysis reaction of one or more organic acids having 6 to 40 carbon atoms, acyl halides having 6 to 40 carbon atoms, or organic acid alkyl esters having 6 to 40 carbon atoms with the above-mentioned polyamines, or wherein said derivatives of polyamines are the reaction products of the condensation reaction of said polyamines with C1-C6 aldehyde, or wherein said derivatives of polyamines are the reaction products of the ammonolysis reaction of an acylating agent containing two acyl groups in a molecule with the above-mentioned polyamines in a molar ratio of 1: (0.5-2), wherein said acylating agent containing two acyl groups in a molecule is one or more of a C6-C30 hydrocarbyl substituted organic dicarboxylic acid, a C6-C30 hydrocarbyl substituted anhydride, and a C6-C30 hydrocarbyl substituted half ester; and wherein the weight ratio of said component (b) to said component (a) is 0.01-100:1. wherein x1 is an integer from 1 to 10, R 4 is H or a hydrocarbyl having 1 to 30 carbon atoms, and R 5 is H or methyl: or a polyene polyamine of the structural formula: H 2 N[(CH 2) x2 NH] y1 R 6 wherein x2 is an integer from 2 to 4, y1 is an integer from 1 to 8, and R 6 is H or a hydrocarbyl having 1 to 30 carbon atoms, and/or a condensate of said polyene polyamine with ethylene oxide and/or propylene oxide; or an imidazoline-type polyamine of the formula; wherein y2 is an integer from 0 to 5, and R 7 is a hydrocarbyl having 1 to 24 carbon atoms; or a piperazine-type polyamine being N-(2-aminoethyl)piperazine or N,N'-di-(aminoethyl)piperazine; or a piperidine-type polyamine: or a tertiary amine containing polyamine of the formula (A 4), (A 5) or: wherein R 9 and R 10 are hydrocarbyls having 1 to 24 carbon atoms, and x4 is an integer from 0 to 10; or wherein x5 is an integer from 1 to 10; or wherein R 11 is a hydrocarbyl having 1 to 24 carbon atoms, and x6 is an integer from 1 to 10, and preferably an integer from 2 to 6; wherein said derivatives of polyamines are the reaction products of the ammonolysis reaction of one or more organic acids having 6 to 40 carbon atoms, acyl halides having 6 to 40 carbon atoms, or organic acid alkyl esters having 6 to 40 carbon atoms with the above-mentioned polyamines, or wherein said derivatives of polyamines are the reaction products of the condensation reaction of said polyamines with C1-C6 aldehyde, or wherein said derivatives of polyamines are the reaction products of the ammonolysis reaction of an acylating agent containing two acyl groups in a molecule with the above-mentioned polyamines in a molar ratio of 1: (0.5-2), wherein said acylating agent containing two acyl groups in a molecule is one or more of a C6-C30 hydrocarbyl substituted organic dicarboxylic acid, a C6-C30 hydrocarbyl substituted anhydride, and a C6-C30 hydrocarbyl substituted half ester; and wherein the weight ratio of said component (b) to said component (a) is 0.01-100:1.