The rate constants for the quenching of biacetyl phosphorescence by a series of conjugated dienes were measured. 1,3-cyclohexadiene (k(qP) = 2.94 x 10(9) s (1) mol (1) L), 2,5-dimethyl-2,4-hexadiene (k(qP) = 1.91 x 10(9) s (1) mol (1) L), 2,4-dimethyl-1,3-pentadiene (k(qP) = 1.78 x 10(8) s (1) mol (1) L), 3-methyl-1,3-pentadiene (k(qP) = 1.22 x 10(8) s (1) mol (1) L), 2,4-hexadiene (k(qP) = 1.35 x 10(8) s (1) mol (1) L) and trans-2-methyl-1,3-pentadiene (k(qP) = 3.84 x 10(8) s (1) mol (1) L). Cyclooctene also quenched biacetyl phosphorescence but with a lower rate (k(qP) = 1.97 x 107 s (1) mol (1) L). Quenching was not observed with 1-methylnaphthalene. Since conjugated dienes quench biacetyl phosphorescence preferentially, this method was studied using gasoline samples with known diene composition. A good correlation was found between the rate of quenching of biacetyl by the gasoline samples and the quantity of conjugated dienes present. (C) 2011 Elsevier Ltd. All rights reserved.