Focusing on the interaction between national brands and private labels, this paper has two main empirical contributions: i) a simultaneous system of demand (share), price and expenditure equations is estimated, and ii) differences in the structure of the local geographic market are incorporated into the analysis. The former represents an important step in understanding the complete nature of private label and national brand interaction, while the latter is important for understanding the impact of the local retail environment on market behavior. IRI scanner data from 1991 and 1992 are used to estimate the three-equation system across 135 food product categories and 59 geographic markets. The results suggest that concentration at both the manufacturer and retailer level can significantly affect private label and national brand price. However, while increased retailer concentration is associated with higher national brand and private label prices, higher manufacturer concentration is associated with higher national brand but lower private label prices. Increases in national brand advertising has the effect of raising national brand price and share, but lowering private label price and share. This is consistent with previous research and suggests that advertising and local market conditions play a significant role in the ability of national brands to price at a premium over private labels. Finally, marketing decision variables such as display activity and private label distribution can have an important impact on total category expenditure.