This thesis was conducted at Siemens Industrial Turbomachinery (SIT) under a period of ten weeks. Siemens service department at this company takes care of the aftermarket of the turbines and provides inspection, spare parts and measures to increase the efficiency of the machines. SIT provides also oil lubrication systems. Because the turbomachines have a variety of pipe systems and flows, it may need to perform flow measurements for troubleshooting, optimization and detection of oil leaks. Through the years, SIT has gathered data from flow measurements that may suggest that a tubomachine system is operating at over or under the designed capacity. However, SIT does not have enough knowledge about proper flow measurements, evaluation of the test results and necessary measures to be taken, therefor no clear work instruction has been established. The goal of this work is therefore to provide a document about applicable flow measurement methods, based on which the company at a later phase can establish necessary work instruction. In order to write this document, necessary theory was gathered in order to understand how oil lubrication systems and flow measurement systems work. The author and some of SIT employees attended a training course in portable ultrasound measurement system provided by PEMA Control AB in Gothenburg. After the course, practical data collection and a summary of the entire flow measurement process was documented. This process was later tested in two experiments. The experiment results, as well as the practical measurement steps were then analyzed and discussed. After the analysis and evaluation a proposal of measurement procedure was compiled. Conclusions of the report include recommendations for improvement of the measurement process. The recommendations include necessary information about what the staff should think about before-, during- and after the measurement. This is to make the measurement as efficient as possible and to minimize the risk of engine failure and personal injuries. Other recommendations were to add necessary equipment to the existing flow measurement bag.