Oscillator strengths and transition probabilities for transitions among the fine-structure levels in Mg-like P IV, S V, Cl VI, and Ar VII are calculated within the weakest bound electronic potential model theory. Our results are discussed and compared with the calculations and experimental values. Oscillator strengths for 3s3d(3)D(J)-3s4f(3)F(J)(0), and 3s4d(3)D(J)-3s4f(3)F(J)(0), transitions, for which very few results exist, are also computed. (C) 2004 Elsevier B.V. All rights reserved.