The mathematical conditions representing the gas liquid critical points of multicomponent mixtures are used to compute the gas liquid critical points of diamagnetic gas condensate fluids of interest to the oil industry, where the effect of a static magnetic field on calculated critical points is studied for the first time. Magneto-chemical fugacity derivatives, required to fulfill the quadratic and cubic forms of the Helmholtz free energy at the critical points, have been obtained from a recently developed theory of phase equilibria in diamagnetic multicomponent fluids and numerical differentiation (Canas-Marin, W. A.; Ortiz-Arango, J. D.; Guerrero-Aconcha, U. E.; Lira-Galeana, C. AIChE J. 2006, 52 (8), 2887-2897). Results in diamagnetic synthetic gas condensate mixtures show that a magnetic field can increase or decrease the critical points depending on mixture. composition and the extent of the applied magnetic field. For mixtures rich in heavy diamagnetic substances (i.e., hydrocarbon oils), the critical points have an initial tendency to decrease up to a certain value of the field and then to increase with the applied magnetic field. If high amounts of light diamagnetic components are present (i.e., gases), the critical properties always increase with the applied field. The effect of the applied magnetic field on the stability limit of these mixtures is also studied in detail.