Experimental specific isochoric heat capacities�iCv�jand PƒÏT�@properties�@for isobutane�@are presented that were measured with a twin-cell type adiabatic isochoric calorimeter.The measurements were obtained for temperatures from 272 to 408K and for pressures up to 30 MPa.The sample purity was 99�D99mol�“�DThe expanded uncertainties�ii.e.�Ca coverage factor k��2�jare �}13mK for temperature�C�}8kPa for pressure�C �}0�D16�“ for density�Cand�}3�D6�“ for Cv in the liquid phase�D An evaluation and a comparison of the expenmental data with highly reliable equations of state confirmed satisfactorily the thermodynamic consistency of the present measurements.