Experimental M-shell nickel spectra in the 14.4–16.5 nm region from the JET tokamak(from both divertor and limiter configurations) and from the reversed field pinch RFX havebeen simulated. These spectra include lines from five ionization states, namely from K-likeNi9+ to P-likeNi13+ ions.For the JET limiter configuration the spectrum upper wavelength limit was higher (18.0 nm) and lines fromSi-like Ni14+ ions were also observed. Collisional–radiative (CR) models have been built forthese six Ni ions, considering electron collisional excitation and radiative decayas the main populating processes for the excited states. These models givephoton emission coefficients (PECs) for the emitted lines at electron density(ne) andtemperature (Te) values corresponding to the experimental situations. Impurity modelling is performed using a1D impurity transport code, calculating the steady state radial distribution of the Ni ions. TheNi line brightnesses are evaluated in a post-processing subroutine and simulated spectra areobtained. The spectrum from a single ion, in the absence of blendings, depends only on theTe and ne values in the emitting shell of the ionization state considered. On the other hand, thesuperposition of these spectra depends on the experimental conditions, as a consequence ofthe fact that the ion charge distribution depends not only on the radial profiles ofTe and ne, but also on the chosen ionization and recombination rate coefficients and on the radialprofiles of the impurity transport coefficients in the region of the emitting shells. Since theaim of the paper is the investigation of the atomic physics of the M-shell ions, the sectiondiscussing the plasma physics phenomena is purposely limited. For each experimentalspectrum a few simulations are presented, since a unique choice has not beenfound by selecting the input parameters of the transport code. The effect of theTe and ne values on the emitting shells as well as the influence of line blendings on the single-ionization-degreespectra are stressed. These, in turn, are then compared with the predictions. For thene range considered the PECs are practically independent ofne.The Te dependence is much reduced due to the fact that the spectral fits performed are actuallycomparisons of line ratios. The agreement found between experimental and simulatedsingle-ionization-degree spectra gives confidence in the atomic data used in the CR models.