Co-branded advertising, where advertisements feature two partnered brands from different categories, should ideally benefit both brands. We test this assertion by studying the effect of featuring a second brand in advertisements on ad and brand name memorability, and the role of category context on which brand is recalled. Our test covers online display advertisements for consumer-packaged brands paired with charity and retailer brands in three markets (USA, UK, and Australia). Independent sample comparisons across 54 brand pairs show that advertising two brands has a neutral effect on ad memorability and negative effect on brand memorability. Furthermore, the advertisement's category context determines which of the brands is recalled. Our findings support a competitive interference theory of dual-brand processing, whereby the two brands compete for attention resources. The results have implications for the return on investment from advertising expenditure, which will vary substantively depending on whether the costs of advertising are shared or borne by one brand in the pair.