The manufacturing control systems are complex. In order to develop manufacturing process control applications rapidly, practitioners rely on the existing commercial enable software such as manufacturing execution systems, supervisory control and data acquisition systems. The enable software has evolved to provide powerful application development tools such as drag-and-drop graphical programming environment. However, the enable software must be interfaced with equipment controllers and other applications since single product is rarely sufficient to support all the functionality required by a process control application. Therefore, the ability of equipment controllers and enable software to interoperate with other components determines the effort required for system integration. This research is to address this ability, also referred to as interoperability. The ability is defined in general terms of service levels and is related to the effort required to achieve categories of process control applications. The methods for qualitative analysis of interoperability will be presented. The method can be used to estimate effort required in system integration in a systematic manner, to provide reference in the development of new process control systems, and to develop reusable software modules. The methods are illustrated with two case studies at the Manufacturing Research Center in Georgia Institute of Technology.