The ground state rotational spectrum of the near-spherical top molecule S 18 O 2 F 2 (sulfuryl fluoride) has been measured from 50 to 700GHz. As for the parent isotopologue, S 16 O 2 F 2 [K. Sarka, J. Demaison, L. Margulès, I. Merke, N. Heineking, H. Bürger, H. Ruland, J. Mol. Spectrosc. 200 (2000) 55–64], it was necessary to use a non-reduced Hamiltonian in order to obtain a satisfactory fit. It was possible to determine six quartic centrifugal distortion constants (instead of five for a standard asymmetric top) and five sextic constants (one of them not existing in the reduced Hamiltonian) could also be determined. This ground state level has also been analysed thanks to a tensorial formalism developed in Dijon. Only two tensorial sextic constants are fixed to zero, all others have been adjusted. Although S 18 O 2 F 2 is less spherical than S 16 O 2 F 2 , the analysis was more difficult. It is partly due to the fact that S 18 O 2 F 2 is oblate whereas S 16 O 2 F 2 is prolate. The experimental quartic centrifugal distortion constants were found in good agreement with those calculated from the force field, confirming the correctness of the analysis.