It has repeatedly been stated that the outcomes of a firm’s alliance portfolio are influenced by characteristics of the partners (Saxton, 1997; Dasí-Rodríguez and Pardo-del-Val, 2015; Jiang et al., 2010). For alliance managers and top management teams, it is necessary to know how different portfolio configurations influence the organization’s outcomes (Leeuw et al., 2014). We study a rarely analyzed type of partner characteristics, portfolio internationalization, which has been shown to substantially impact firm performances (Zaheer and Hernandez, 2011; Lavie and Miller, 2008; Goerzen and Beamish, 2005). In our globalized world, alliances are increasingly international. Consequently, it is a key issue for firms to determine the optimal degree of alliance portfolio internationalization (API). However, studies pursuing this question concentrated on innovation driven exploration alliances and found an S-shaped relationship between portfolio internationalization and firm performances (Lavie and Miller, 2008). Less attention has been devoted to the internationalization of exploitation alliance portfolios. Exploitation alliances refer to agreements where the focus is put on the usage of existing resources and information (March, 1991). In many industries like air transport (Casanueva et al., 2014) or biotechnology (Rothaermel, 2001) they are used frequently and have a strong impact on firm performances. Compared to exploration alliance, they influence firm performances differently. Learning and innovation play only a minor role in exploitation alliances (Vassolo et al., 2004; Rothaermel, 2001). They affect operations more directly compared to the lagged impact of product development through exploration alliances (Yamakawa et al., 2011). Hence, exploitation alliances are less uncertain and more predictable (Levinthal and March, 1993; Nielsen and Gudergan, 2012). They offer a more “beaten track,” because the inputs and outputs are often well-known (March, 1991). The necessary tasks in exploitation alliances are therefore more standardized. Consequently, it is reasonable to assume that the internationalization of exploitation portfolios also affects firm performances in a unique way. We predict a U-shaped impact of API on firm performance in the context of exploitation alliances. Hence, we do not expect a decline of performances at high levels of portfolio internationalization as overserved in the study of Lavie and Miller (2008), which we use as a role model for our study.