We report results of theoretical studies of 3s → np and 2s → np autoionization resonances, respectively, in the 3p and the 2p photoionization cross sections of a few members (Ar, K +, Ca 2+, Fe 8+, Zn 12+, and Kr 18+) of the argon isoelectronic sequence, within the framework of the relativistic random phase approximation and using the relativistic multichannel quantum defect theory. The present approach would enable analysis of complex atomic spectra especially of atomic and (or) ionic species that are found in stellar gases in a computationally economical way. The shape profiles of the autoionization resonances have been analyzed in the present work using appropriate Fano parameters. The quantum defects determined for some of the lower or intermediate excited states are found to be in good agreement with the experimental and (or) theoretical results. © 2012 Published by NRC Research Press.