The hydroalkoxycarbonylation of styrene was carried out by using various alcohols (ethanol, n- and i-propyl alcohol, benzyl alcohol, n-octyl alcohol) in imidazolium-based ionic liquids. In addition to the formation of the expected 2-phenyl- and 3-phenyl-propionates, the oligomerization of the substrate depending on the reaction conditions was also observed in [BMIM][PF6] and in [BMIM][BF4] (to a small extent) ionic liquids. Moderate to high regioselectivities towards branched esters have been obtained in [BMIMI[BF4]. The highest regioselectivities towards branched ester have been observed with 'preformed' PdCl2(PwPh(3))2 catalyst. The addition of diphosphines favoured the formation of the linear isomer. The application of [BMIM][PF6] ionic liquid results mainly in the formation of the linear esters. The regioselectivity is strongly dependent also on the alcohol: for example, while the application of ethanol resulted in branched regioselectivities up to 50 and 81% in [BMIM][PF6] and [BMIM][BF4], respectively, 100% linear and 83% branched selectivities were obtained in the presence of n-octyl alcohol as a nucleophile. (c) 2005 Elsevier B.V. All rights reserved.