This empirical study explores the different factors influencing the runtime of a booking process in the middle office of a major European investment company. The study is based on mixed methods research that combines qualitative research data collection techniques with a quantitative research approach. On the basis of semi-structured interviews, we first develop and present a model of the business process and control points to assess booking runtime. We further identify relevant and IT-related factors such as process automation that may affect booking runtime. Then, we analyze a unique dataset of historical process cycles providing details on booking runtime. Our quantitative analysis of this data provides new insights into how to identify most relevant factors affecting runtime of transaction processes in the financial industry. From a methodological perspective, our study illustrates how to conduct mixed methods research in the field of process performance evaluations.