Excess molar enthalpies, H-ijk(E) of ternary 1-ethyl-3-methylimidazolium tetrafluoroborate (i) + Pyrrolidin-2-one (j) + Pyridine or Water (k); 1-ethyl-3-methylimidazolium tetrafluoroborate (i) 1-methyl pyrrolidin- 2-one (j) + Pyridine or Water (k) and H-E of Pyrrolidin-2-one (i) + Pyridine or Water (j); 1-methyl pyrrolidin-2-one (i) + Pyridine (j); 1-ethyl-3-methylimidazolium tetrafluoroborate (i) + Water (j) mixtures have been measured over entire mole fraction range at 298.15 K. The H-ijk(E) value for 1-ethyl-3-methylimidazolium tetrafluoroborate (i) + Pyrrolidin-2-one (j) + Water (k); 1-ethyl-3-methylimidazolium tetrafluoroborate (i) + 1-methyl pyrrolidin-2-one (j) + Pyridine or Water (k) are positive over whole range of composition and for 1-ethyl-3-methylimidazolium tetrafluoroborate (i) + Pyrrolidin-2-one (j) + Pyridine (k) mixture, the sign of H-ijk(E) values varies with change in composition of the components. The observed data have been analyzed in terms of (i) Graph; and (ii) Prigogine-Flory-Patterson (PFP) theories. Results indicate that H-E and H-ijk(E) values obtained by Graph theory are in good agreement with experimental data. The PFP theory correctly predict sign as well as magnitude of H-E values for the binary mixtures. However, theory fails to predict the sign of H-ijk(E) values for the ternary mixtures. (C) 2013 Elsevier Ltd. All rights reserved.