This paper examines how audit oversight by a public-sector regulator affects investors’ assessments of reporting credibility. We analyze whether the introduction of the Public Company Accounting Oversight Board (PCAOB) and its inspection regime have strengthened capital- market responses to unexpected earnings releases, as theory predicts when reporting credibility increases. To identify the effects, we use a difference-in-differences design that exploits the staggered introduction of the inspection regime, which affects firms at different points in time depending on their fiscal year-ends, auditors, and the timing of PCAOB inspections. We find that capital-market responses to unexpected earnings increase significantly following the introduction of the PCAOB inspection regime. Corroborating these findings, we also find an increase in abnormal volume responses to firms’ 10-K filings after the new regime. Overall, our results are consistent with public audit oversight increasing the credibility of financial reporting.