We provide evidence that distinguishes between competing production cost-based explanations of how to interpret unusually high (or low) audit fees and their expected relation with accounting quality. Abnormally high or low fees are typically proxied by the residuals obtained from fee models. Whereas prior research assumes these residuals are independent from one year to the next, we argue that the inherent “stickiness” in audit fee residuals also means that measures of unexpected fees will be serially correlated. Our results strongly support this view, and suggest that audit fee residuals reflect a limitation of the standard audit fee model in capturing attributes of the auditing environment that are not well captured at the client-firm level. However, we also argue that the extent to which residual fees differ from the recent past can clarify their relation to accounting quality. We show that the “jump” in fee residuals relative to their long-run “sticky” average is strongly associated with lower accounting quality. Hence, a “jump” in fee residuals is a suitable proxy for lower accounting quality, as it likely reflects reactive auditor effort and/or an additional risk premium. We then show that long-run fee residuals are also negatively associated with subsequent accounting quality, a result which further contradicts the argument that higher abnormal audit fees capture increased proactive effort and therefore reflect “investments in auditing”. Overall, our results suggest that risk, rather than proactive effort, is a better explanation for higher than expected audit production costs.