A pharmaceutical formulation comprising at least one omega-3 polyunsaturated fatty acid in free acid form or a pharmacologically acceptable derivative thereof is contained in a soft gelatin capsule characterised in that the capsule comprises gelatin extracted by an extraction process comprising acid pre-treatment of a collagen source. One advantage of the present invention over a soft to gelatin capsule containing the same formulation but comprising gelatin extracted by an extraction process comprising alkali pre-treatment of the collagen source is that the present invention does not harden significantly over time and thus has a longer shelf life.