Complementary products or services may belong to the same market or to different markets, as the case may be. When the supply and demand stem from different operators and are related to specific products or services, the different stages of the same economic process constitute distinct markets. It is thus possible to distinguish the market of the raw materials necessary for the manufacture of a product from the market on which the product is sold, consumables from devices with which they are compatible or new tires from retreaded tires.

Where the user benefits from an additional service, a specific market exists. Such is the case of mobile or car phones that are distinct from traditional phones, services indispensable to professional dealers in respect of the sale of cars or an antibiotic from other products of the same type insofar as it is part of the modern therapeutic compositions most frequently used to treat a particular type of disease.

In the specific case of a secondary market complementary to a primary market, the supervisory authorities had to consider that an undertaking may be in a dominant position regarding its own products where the market of the secondary product is a captive market. Such is the case where access to the secondary market is prohibited to third party undertakings due to the fact that the dominant undertaking holds an intellectual property right. More generally, the Commission considers that a narrow definition of the secondary product market is relevant when the compatibility with the primary product is important.