Walmart is not a good example of perfect competition. First, Walmart does not sell an identical product as all of its competitors because the different competitors carry different lines of products and different overall product offerings (ie some offer groceries while others don't). In addition, there are only a few firms in the market (namely Target). This lack of competition exists because there are high barriers to entry in the market. Specifically, the need to produce a high quantity in order to keep prices low prevents many firms from entering the market since they are unable to capture a large enough portion of the market to have competitive pricing. Based on all of this information, Walmart would most likely fit into the oligopoly market structure.