Channel expansion theory predicts positive relationships between knowledge-building experiences and perceptions of a medium's capacity for conveying complex information. To date, channel expansion has only been tested in a pair of studies focused upon perceptions of a single medium-email. The present investigation replicates the initial tests of channel expansion theory, assesses the validity of the theory for two additional media, examines whether differences in media explain additional variation in richness perceptions, and analyzes the relationships between expansion predictors and dimensions of richness across three media. Data from 529 organizational media users revealed the following: (1) knowledge-building experiences with a medium, communication partner, topic, and social influences are positively related to perceptions of a medium's richness, (2) these relationships are fairly consistent across email, telephone, and face-to-face, (3) differences in richness are attributable to differences between media, and (4) expansion variables appear to be selectively related to richness dimensions and these relationships vary across media.