Over the last decades, alliance portfolio has been an important research area within the management and international business fields. Since engaging in multiple alliances provides many advantages to firms, the extant literature rather highlights the positive side of alliance portfolios. But, at the same time, focal firms of alliance portfolios sometimes suffer from competitive relations among their partners. By applying a competitive embeddedness lens, we examine the influence of competitive relations among partners within an alliance portfolio on the focal firm's alliance formations. Also, we examine the role of the focal firm's resources which moderate the relation between competition among its partners and its alliance formations. We investigated 2539 cases of global technology alliances in the biopharmaceutical industry from 2002 to 2006 through negative binomial regression. Our findings indicate that a holistic approach toward alliance portfolios to prevent competition among partners is significant for sustainable alliance strategies. Moreover, we suggest that firm resources which attract partners also lessen the impact of competition among alliances.