We have calculated the energy levels, oscillator strengths, and transition probabilities for eight carbon-like ions (Na vi, Mg vii, Al viii, Si ix, P x, S xi, Cl xii and Ar xiii) using the Hartree–Fock pseudo-relativistic (HFR) and Thomas–Fermi–Dirac–Amaldi (TFDA) approaches. We used configuration expansions containing eight configurations, namely 2s2 2p2, 2s 2p3, 2s2 2p 3s, 2s2 2p 3p, 2s2 2p 3d, 2s2 2p 4s, 2s2 2p 4p, and 2s2 2p 5s. For each of the considered ions we obtained 59 energy levels, a number of which are not in the National Institute of Standards and Technology (NIST) data base. We compared our results with critically selected experimental data from NIST and with calculations made using the multiconfiguration Hartree–Fock (MCHF) method. We calculated weighted oscillator strengths and transition probabilities using two methods (HFR and TFDA) for the 2s2 2p2 and 2s 2p3 configurations for the eight C-like ions considered here. We analysed the atomic structure parameter trends, which allowed us to find missing data belonging to an isoelectronic sequence. The energy levels, oscillator strengths, and transition probabilities calculated here are in good agreement with the data from the NIST data base. Because emission and absorption features from C-like ions are often used for density and temperature diagnostics of various plasmas in astrophysics, and in studies of the solar corona, including solar flares, and of the coronae of other stars and of ionized outflows in active galactic nuclei etc., the obtained data will be useful for improving plasma diagnostics and modelling, in particular for the X-ray Universe.