To compare the generalizability of online and mail surveys in a cross-national service quality study, the authors use G-theory and find a comparable level of generalizability, though online surveys benefited from considerably lower costs. This article contributes to the current comparison of the response quality between online and mail surveys. Furthermore, the authors illustrate how G-theory can be used to compare online and mail surveys and take data collection costs into account. Important implications include the process and results of comparing two survey modes and the effects for service research.