Organic Rankine Cycle (ORC)-based systems are being extensively investigated for heat-to-electric power conversion from various sources, such as biomass, waste heat recovery, concentrated solar thermal and geothermal. The ORC technology has a promising future as it helps to meet energy requirements, arguably with a minimal environmental impact. This work summarizes the current state-of-the-art of actual i.e., experimental ORC system performance, derived from a comprehensive analysis of the most significant, relevant and up-to-date experimental data published in scientific literature. A survey of more than 200 scientific works is scrutinized according to specific selection criteria and data is extracted to develop a database containing thermodynamic cycle information along with component-level performance information. Performance trends are discussed and addressed as functions of first principles. One of the least surprising results indicate that the performance follows economies of scale. More revealing is the fact that the Organic Rankine Cycle conversion efficiency (mechanical to electrical) was around 70%. Furthermore, it becomes clear that there is a large gap between research and development for source and sink temperature differences above 150 °C. In general, the overall heat to electrical power conversion efficiency was around 44% of the Carnot cycle efficiency of the cycle. A host of other relevant thermodynamic parameters are cross-compared, as well as compared to theoretical results, allowing a level of practical ORC system design target homologation to be achieved which is useful for the engineer as well as the scientist in the design of ORC components, systems as well as advanced cycles.