This paper develops a method for market definition using demand-and-supply estimations. That method is then applied to the Argentine dishwashing detergent industry, using data from the years 2022-2024. The results are compared to the ones obtained using only demand estimations, and the conclusion is that the use of supply price equations generates a considerable improvement in those results. Through our empirical estimations, we also find that the dishwashing detergent industry in Argentina seems to be divided in two relevant markets: one that includes the two main detergent brands, and another one that encompasses the remaining brands.