Three ruthenium catalysts were investigated for the metathesis reaction of methyl soyate. Dichlorotris (triphenylphosphine) ruthenium 11 and his (tricyclohexyl phosphine) benzylidine ruthenium (IV) dichloride displayed no reactivity at 40 degrees C and atmospheric pressure. However, ruthenium [1,3-bis-(2,4,6-trimethylphenyl)-2-imidazolidinylidene] dichloro (phenylmethylene) tricyclohexylphosphine, Grubbs second generation catalyst, exhibited high activity at these mild conditions. After 2 h, 46% of the unsaturated methyl esters in a commercial methyl soyate were metathesized. This suggests a method to modify the structure of methyl soyate to improve diesel fuel performance properties. (c) 2005 Elsevier Ltd. All rights reserved.