<p>Fault-related folds frequently serve as structural traps for hydrocarbons, and the orientation of the principal stress axes can be used to determine the optimal drilling direction. The present study investigates the effects of geometrical variations along the strike of detachments and ramps on the orientation of the principal stress axes in fault-related folds. For this purpose, three series of 3D finite element models are presented. The results show that in all models, the orientations of the principal stress axes and of maximum stress contours reflect the detachment or ramp geometry. Also, in all models, σ₁ and σ₂ are horizontal and are parallel and perpendicular to displacement, respectively, while σ₃ is vertical. However, the three stress axes rotate in fold crests and limbs, and the geometry of the detachment or ramp controls the rotation. In models with frontal and oblique detachments or ramps which produce inclined or plunging folds, its horizontal component of σ₁ is parallel to displacement in both fold limbs and crests; but in models with wavy detachments or ramps which produce double plunging folds, this condition exists only at the fold crest. In models with wavy detachments or ramps, minimum rotation of the local σ₁ is observed at the fold crest and maximum rotation in the limbs. These results show good agreement with the modelled structural geometry of the Ahwaz anticline (Dezful Embayment, SW Iran) which is a important structural trap for hydrocarbons.</p>