Semi-crystalline polymers are widely used in industrial applications, e.g. in beverage containers, plastic bags, etc. In many applications, the fracture mechanics properties are of great interest, e.g. in the opening procedure of beverage containers. The present work focuses on experimental measurement of the energy release rate in these polymers. A fairly simple multi-specimen experimental method is proposed that makes use of the stored elastic energy in the structure. By use of this method, the energy release rate is estimated to about 1.6 kJ/m2 for the polymer in question.