This note focuses on the theoretical relationship between price and generic advertising when supply is uncontrolled and markets are Interrelated through consumer preferences. A key finding is that the mutatis mutandis relationship between own-price and own-advertising is indeterminate unless the structural elasticities pertaining to own-price and own-advertising effects are greater in absolute value than the corresponding cross elasticities. This implies, inter alia, that benefit-cost analyses based on single-equation models may overstate producer returns to generic advertising, a conclusion verified in the empirical application.