This paper presents a simple method for screening competition in differentiated products oligopoly with a small number of competitors. In many situations, estimation of price elasticities of demand may be impossible due to difficulties in defining demand or missing data on sales. However, even without information on price elasticities, in certain situations it is possible to test for the static non-cooperative Nash-Bertrand equilibrium, which in the case of rejection, may be important screening information for antitrust authorities. The static non-cooperative Nash-Bertrand equilibrium may be rejected when demand is linear and in the estimation of best-response functions, the coefficients on the competitors' prices are statistically greater than 0.5. The application of this method is illustrated by the example of German mobile telephony using monthly data between January 1998 and December 2002. According to the estimation results, the observed prices in the segment of low-users cannot be the outcome of a static non-cooperative Nash-Bertrand equilibrium.