Advocate General Kokott (AG) recently gave an interesting Opinion on when a concerted practice may have an anti-competitive object. The case (C-8/08) came before the European Court of Justice (ECJ) on a preliminary reference from a Dutch court in a case concerning an exchange of information by mobile phone operators on dealer commissions. On the question of when an exchange of information may amount to an anti-competitive concerted practice, the AG took the view that it is necessary to consider the legal and economic context to determine if the exchange is capable of removing existing uncertainties of the parties' intended market conduct. The standard of proof which is required is a matter of national law, provided that the principles of effectiveness and equivalence between national and EU law are met. With respect to effectiveness, this means that proof should not be so onerous that it is excessively difficult to prove. In practice there would be a presumption of a causal link between participation in concerted actions between competitors (such as the exchange of sensitive information) and their actions on the market. That presumption however is subject to the ability of the undertakings concerned adducing evidence to the contrary. The AG was also of the view that proof of collusion does not require evidence of a lengthy practice, even an isolated exchange of information between competitors may result in an alteration of the market conduct of the participants.