Energy levels, lifetimes, oscillator strengths and transition probabilities for the multicharged oxygen like Cl X ion have been calculated with the configuration expansion: 2s 2 2p 4 , 2p 6 , 2s 2 2p 3 3p, 2s2p 5 , 2s 2 2p 3 3s, 2s 2 2p 3 4s, 2s 2 2p 3 3d, 2s 2 2p 3 4d, 2s2p 4 3s and 2s2p 4 4s. We used two methods in the calculations: the Hartree– Fock pseudo-relativistic approach and the Thomas–Fermi–Dirac–Amaldi potential approach using the Cowan and the AUTOSTRUCTURE atomic structure codes respectively. Results have been compared with available ex- perimental data from the National Institute of Standards and Technology Atomic Spectra Database (NIST-ASD) and with results from other available calculations. There is a great lack of atomic structure data of Cl X and obtained new data will be important for physics applications and astrophysical modeling.