67Article 81(1)(a) and (b) EC expressly declare that agreements and concerted practices which consist in directly or indirectly fixing purchase or selling prices or other transaction conditions or in limiting or controlling production or outlets are incompatible with the common market. Infringements of that kind, particularly in the case of horizontal cartels, are classified by the case-law as ‘particularly serious’ since they involve direct interference with the essential parameters of competition on the market in question (Case T-141/94Thyssen Stahl v Commission [1999] ECR II-347, paragraph 675) or clear infringements of the Community competition rules (Case T-148/89Tréfilunion v Commission [1995] ECR II-1063, paragraph 109, and Case T-311/94BPB de Eendracht v Commission [1998] ECR II-1129, paragraph 303).