In this paper we are concerned with the development of an observational research approach to gain insights into the performance of Business Process Modelling Methods (BPMMs) in practice. In developing this observational approach, we have adopted an interpretive research approach. More specifically, this involved the design of a questionnaire to conduct semi-structured interviews to collect qualitative research data about the performance of BPMMs. Since a BPMM is a designed artefact, we also investigated Design Science Research literature to identify criteria to appreciate the performance of BPMMs in practice. As a result, the questionnaire that was used to guide the interview is based on a subset of criteria of progress for information systems theories, while the observational research approach we adopted involves the collection of qualitative data from multiple stakeholder types. As a next step, the resulting questionnaire was used to evaluate the performance an actual BPMM in practical use; the DEMO method. Though the analysis of the collected qualitative data of the DEMO case has not been fully performed yet, we already foresee that part of the information we collected provides new insights compared to existing studies about DEMO, as is the fact that a variety of types of stakeholders have been approached to observe the use of DEMO.