Given the important economic consequences of an oil platform failure, all the aspects of its structural behavior and safety issues need to be carefully considered. In particular, P-D effects on the deck legs of marine offshore jacket platforms may be relevant when the deck height and the vertical load are significant. In this paper, the impact of the moment amplification, due to lenderness of the deck legs, on the platform safety is examined and appraised from he viewpoint of the structural reliability. The formulation is applied to a typical tall deck marine platform under the environmental loading at the Bay of Campeche, Mexico, and its reliability index is calculated with and without the P-D effect. The results presented herein may be sed to improve the current practice in the design and assessment of offshore marine platforms in Mexico and to update the current version of the code.