The effect of ethanol addition to pure gasoline on the solvatochromic band of dyes 2,6-diphenyl-4-(2,4,6-triphenylpyridinium-1-yl)phenolate (1), 2,6-di(4-tert-butylphenyl)-4- [2,4,6-tri(4-tert-butylphenyl)pyridinium-1-yl]phenolate (2), 1-(4-dimethylaminophenyl)-2-nitroethylene (3), and 1-(4-dimethylaminophenyl)-2-nitropropene (4) was investigated. The dyes are very soluble in gasoline-ethanol mixtures. The data show the occurrence of strong preferential solvation of the dyes by ethanol in all mixtures. Solutions of dye 2 are blue-green in gasoline, violet in ethanol, and green-blue in gasoline with 25% of ethanol, which allows a naked-eye detection of the presence of ethanol in gasoline. Also, the use of solvatochromic dyes to develop an analytical method for the determination of the quality of fuels is discussed. (C) 2006 Elsevier Ltd. All rights reserved.