The various articles about standardisation decisions tend to overlook an important phenomenon, that of the competition between a private and a public company (mixed duopoly). Such a competition occurs essentially in international trade. It is the purpose of this paper to study standardisation decisions made in this context. In a model of vertical differentiation, we show that the competition system in which standardisation is the most likely to emerge depends on the degree of differentiation of the intrinsic qualities. If this degree is high and if the public firm sells the best product, then mixed duopoly is more favourable to standardisation; otherwise, when products are then relatively similar, it is public duopoly.