Excess volume and ultrasonic velocity measurements have been carried out for nitromethane (NM), nitroethane (NE), 1-nitropropane (1-NP), 2-nitropropane (2-NP) and nitrobenzene (NB) in gamma -butyrolactam (n = 5), i.e. pyrrolidin-2-one (PY) at 303.15 K over the entire composition range. The VE values are negative for PY + nitroalkanes expect for NM which exhibits S-shaped behaviour. A very small VE is observed in PY + NB. Using ultrasonic velocity and excess volume data, molar isentropic compressibility KS and excess isentropic compressibility K-S(E) have been computed. The results have been analysed in the following sequence. (1) Quantitative estimation of different contributions, viz. interactional, free volume and P* effect to V-E using Prigogine-Flory-Patterson (PFP) theory; (2) the calculation of pat tial molar volumes, apparent molar compressibility and their excess values to gain insight into solute-solvent interactions.