This study examines the competitive price effect of Wal-Mart Supercenters on national brand and private label grocery prices in New England. For this purpose, we use primary price data collected on a basket of identical products from six Supercenters in Massachusetts, Connecticut, and Rhode Island as well as a sample of conventional supermarkets. Taking into account demographics, store characteristics, and market conditions, we estimate the average prices charged by (1) Supercenters, (2) supermarkets competing directly with Supercenters, and by (3) supermarkets geographically distant from Supercenters. By comparing prices at competing stores and at distant stores, we show that the effect of Wal-Mart Supercenters is to decrease prices by 6 to 7 percent for national brand goods and 3 to 7 percent for private label goods. Price decreases are most significant in the dry grocery and dairy departments. Moreover, Wal-Mart sets prices significantly lower than its competitors in the food industry.