We investigate whether the practice of voluntarily engaging two audit partners is associated with audit quality and audit fees. Using a sample of listed Finnish and Swedish firms, we find evidence that joint engagement partners may be associated with higher audit quality, but not with higher audit fees. Moreover, the benefits of having joint engagement partners are driven by the cases where the partners are co-located in the same office and the clients' characteristics suggest the audit will be more challenging than is usual. When the joint engagement partners are from different offices, we find no variation in audit quality from that of single-partner audits, but a small reduction in audit fees. We interpret these findings to suggest that two audit partners co-located in the same office increase the effectiveness of the audit, whereas partners from different offices improve the efficiency vis-à-vis that of a single-partner audit. In general, our findings suggest that the benefits of the “four eyes principle” usually attributed to joint audits between two audit firms, are also applicable when there are two jointly responsible engagement partners from the same firm and, importantly, that the costs to clients do not appear to increase.