Service-oriented computing promises to create flexible business processes and applications on demand by dynamically assembling loosely coupled services within and across organizations. Quality requirements play a central role in service sourcing and, together with Service Level Agreements, facilitate service selection and measurement of service delivery effectiveness. This empowers customers to make better decisions when faced with multiple service offerings and varying service costs. However, existing business process modeling languages provide little support for quality requirements annotation and specification. This paper argues that quality requirements are a central aspect of business process modeling specification, and thus proposes to incorporate time, cost and reliability quality requirements as extensions to the Business Process Modeling Notation (BPMN). These quality requirements are evaluated based on analytical model using reduction rules. An example of online purchasing business process is illustrated to demonstrate the applicability of the proposed approach.