Co-production is defined as customer participation in production activities that generate a result to be consumed (Etgar, 2008). Previous research has shown the positive effects of co-production, such as satisfaction, perceived control, and perceived quality (Chan, Yim, & Lam, 2010; Golder, Mitra, & Moorman, 2012; Hunt, Oneto, & Varca, 2012). However, knowledge about the potential negative consequences from co-production is scarce. Despite the importance of the role of causal locus in the generation of unsatisfactory results, to date, this subject has not been properly studied. Considering that co-production is increasingly common in contemporary consumption contexts, this paper aims to broaden knowledge about unsatisfactory results from co-production. Based on two experimental studies, we analyze the role of the causal locus of failures on customer regret and disappointment, taking into consideration the self-serving bias. The results show that a consumption situation with an unsatisfactory regret tends to be higher when the consumer takes the blame than when the causal locus is attributed to the company. When the causal locus is uncertain, regret is higher than disappointment and higher than the regret experienced when the company or the service employee is blamed. Because regret is associated with internal causal attribution, these results contradict the self-serving bias literature, which affirms that people are more likely to make external than internal attributions for failures (Mezulis, Abramson, Hyde, & Hankin, 2004; Weiner, 2010). The internal failure attribution converges with the idea that consumer participation in production implies more responsibility over the result (Bitner, Faranda, Hubbert, & Zeithaml, 1997; Prahalad & Ramaswamy, 2004).When the causal locus is attributed to the company or to the service employee, disappointment towards the company tends to be higher than in the other conditions and higher than regret. Study 2 tested whether consumers who co-produce would take responsibility for a failure and blame themselves in situations where the causal locus was undetermined. The results once again contradicted the self-serving bias literature in a scenario with co-production. Consumers who co-produced experienced more regret and less disappointment towards the company, and they blamed themselves more intensely than the consumers who did not co-produce. Therefore, the consumers who co-produce take more responsibility for dissatisfying results and, consequently, regret their actions to a higher degree than those consumers who do not co-produce. These results show that even when co-production fails to generate a satisfying result for the consumer, it may be positive for the company because it provides a context in which both the consumer and the company may be responsible for the failure. When the company is blamed, consumers experience less regret and more disappointment towards the company than when the consumer is the one to blame. But when the consumer is blamed or the causal locus is uncertain, situations that are both possible in a co-production context, then consumers experience more regret and less disappointment towards the company.