The long history of evolving energy systems is also the history of adding new forms of flexibility, from run-of-the-river hydropower with limited spatial and temporal flexibility to contemporary fossil-fuel based electricity systems allowing more flexibility due to storable and transportable fuel and controllable generation. The increasing shares of solar and wind energy, which are available everywhere, but not all the time, calls for new types of flexibility strategies. Monitoring changing patterns of flexibility strategies add to our understanding of the status and direction of long run energy system transformation. To capture such broad trends and allow for comparison across regions, this study develops two indicators: Gross spatial flexibility (GSF) and Gross temporal flexibility (GTF). The indicators are tested on a sample of countries including Australia, Germany-Luxembourg-Austria (GLA region), Sweden and the USA. By normalising storage and transmission capacity to average power demand these indicators are shown to enable comparisons across time and across regions of different sizes. At present, publicly available data in most countries remain insufficient for simple indicator construction and continuous updating. The German MaStR platform is an exception and could serve as inspiration for database construction in other countries.