The (liquid + liquid) equilibrium (LLE) of 20 binary systems containing 1-hexyloxymethyl-3-methyl-imidazolium tetrafluoroborate ([C(6)H(13)OCH(2)mim][BF4]) with aliphatic hydrocarbons (n-pentane, or n-hexane, or n-heptane, or n-octane), aromatic hydrocarbons (benzene, or toluene, or ethylbenzene, or o-xylene, or in-xylene, or p-xylene), cyclohexane and 1-hexyloxymethyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)-imide ([C(6)H(13)OCH(2)mim][Tf2N]) in aliphatic hydrocarbons (n-hexane, or n-heptane), aromatic hydrocarbons (benzene, or toluene, or ethylbenzene, or o-xylene, or m-xylerie, or p-xylene) and cyclohexane was carried out by using a dynamic method from T = 290 K to the boiling temperature of the solvent. In this work, a systematic study of the impact of different factors on the phase behaviour of alkoxy-imidazolium-based ionic liquids with hydrocarbons has been presented. All systems examined showed upper critical solution temperature (UCST) behaviour, with low solubility of the ionic liquid in n-alkanes and cycloalkanes and high solubility in aromatic hydrocarbons. An increase in the alkyl chain length of n-alkane, or at benzene ring resulted in an increase in the UCST. The choice of anion was shown to have large impact on the UCST of the system: by changing the anion [BF4](-) to [Tf2N](-), the solubility dramatically increased and the UCST decreased. The relative hydrocarbon affinity for different anions observed was [BF4](-) < [Tf2N](-). The thermophysical characteristic of ionic liquids was detected by differential scanning calorimetry (DSC). mean-square deviation of the equilibrium mole fraction for all the calculated values was 0.0044. (c) 2005 Elsevier Ltd. All rights reserved.