Rovibrational spectra of the C--O stretch band ν5 of Ni(CO)4 have been recorded at 0.006 cm-1 resolution by coupling a low pressure continuous supersonic jet with a high resolution interferometer. The spectrum has been analyzed thanks to the STDS software (see http://icb.u-bourgogne.fr/OMR/SMA/SHTDS/) that implements the tensorial formalism developed in the Dijon group for tetrahedral molecules. We obtain a very satisfying simulation thanks to an effective Hamiltonian expanded up to order 3. The asymmetry of the high-J lines is due to a small tetrahedral splitting and is well reproduced. The root mean square deviation is 0.96 10-3 cm-1. The Coriolis constant is somewhat larger than for other spherical-top carbonyls like Mo(CO)6 and W(CO)6 and, as a consequence, the level structure displays a standard three-branch structure, typical for triply degenerate fundamentals.