Quality of Service (QoS) plays a key role in the successful development of software-as-a-service (SaaS). A quality model needs to be devised for ensuring customers' satisfaction and to set an expected level of quality standards. In this research, several journals and research papers were reviewed, and quality models available for service-oriented architectures (SOAs) were analyzed. A lot of research is done for SOA systems but we need more QoS models for SaaS. In this thesis, the quality attributes for SaaS were examined and reported. An ontology model for QoS in SaaS was also proposed in the thesis. Service level agreements, of companies that implement SaaS, were studied and compared in order to study the current market trends in the field of SaaS quality. This thesis provides a method to compare the QoS of various service providers for SaaS. The implementation of a proposed ontology model will help improve the current standard of quality for software available as a service.