An adiabatic calorimeter was used to measure the enthalpy of solution of 1-octyl-3-methylimidazolium tetrafluoroborate (0.0035 mol(.)kg(-1) to 0.02 mol(.)kg(-1)) in water and in aqueous sodium fluoride of different ionic strengths (0.1 mol(.)kg(-1) to 0.43 mol(.)kg(-1)) at nominal temperatures of 298 K, 306 K, and 313 K. Two additional measurements of the enthalpy of solution of 1-butyl-3-methylimidazolium tetrafluoroborate (0.013 mol(.)kg(-1)) in water at 298 K are also reported. The present results lead to the standard-state changes of enthalpy and heat capacity for the solution process. The contribution of a methylene group to the enthalpy of solution of these ionic liquids was determined from the measurements and is shown to be in agreement with the value obtained from other classes of organic compounds. The enthalpy of solution increment for the methylene group is used to calculate the enthalpy of solution of the series of 1-alkyl-3-methylimidazolium tetrafluoroborates. Calculated standard-state heat capacity values for the aqueous solution process and the aqueous solute are also given. Potential micelle formation of 1-octyl-3-methylimidazolium tetrafluoroborate in water was examined.