An econometric model is developed and used to estimate price promotion effects on sales for the yogourt category in a Quebec market. More specifically, the paper assesses the impact of a price cut on: (1) current sales of the promoted product, (2) future sales of the promoted product itself and competing ones in the category (own and cross displacement effects), (3) current sales of other sizes of the same brand (brand's cannibalization effects), and (4) sales on other brands' sales for each available size (substitution effects or category's cannibalization effects).