The article concerns standards of economic analysis in antitrust cases based on the example of the case on concerted actions (article 11 of The Federal Law No. 135-FZ ‘‘On the Protection of Competition’’, which became enforced on 26 July, 2006). Using economic theory and quantitative analysis of the results of the auction, the article offers a methodological approach to the analysis of parallel behavior of participants of an auction. The development of new methodological approaches is necessary for the antitrust law enforcement when behavior of companies cannot be qualified as illegal per se. The analysis of the parallel behavior of participants of the auction consists of three main parts: the revelation of external factors that could have caused the parallel behavior of companies; the description of the companies’ motivation caused by these factors that could have led to the observed behavior; quantitative analysis of the probability of such motivation. According to the results, parallelism that was observed might have been not the consequence of collusion but have been caused by external economic factors. Based on the data of the results of the tender for the right to install advertising constructions in one of the Russian cities, using mathematical analysis, probability theory, game theory and mathematical statistics, it was shown how the existing market conditions could have led to the observed behavior of companies; and the probability of such behavior without collusion was estimated. The idea of the structure of economic analysis offered in this work can be employed in the wide range of antitrust cases on cartels and concerted actions.