In order to survive and prosper in the ever-changing global competition companies are focusing on their core competencies, resulting in the outsourcing of non-core functions. A growing trend in outsourcing is business process outsourcing (BPO) which involves contracting the operations and responsibilities of specific business processes to a third-party service provider. The key ingredient to a successful BPO contract is a service level agreement (SLA) that defines the expectations and requirements of both parties and is supported by a set of performance metrics. However, there is relatively little empirical research that attempts to develop SLA indicators suited for BPO services. Therefore, in this paper we extracted SLA indicators for BPO based on literature review and then classified them into the four perspectives of the balanced scorecard (BSC) framework through a modified Delphi process. We also examined empirically the causal relationships between each indicators pertaining to the four BSC perspectives, using partial least squares (PLS) analysis. It is expected that this study can serve as a good reference for both BPO service providers and users in developing and applying SLA indicators.