Thx. the explanation. Now I mostly understand the concept. Yes, it is quite well simulates the "oil boom" in mankind history. More questions. Coail liquifer produce the same oil spill resource that is extracted from wellls? If I have 3 in different cities how it is distributed among different cities? All oil dependen special building in a city requires the spill resorce within the citiy borders?l What about resoruces that an ally or city state has? If he trade or share the oil does it functional as a spill resource? Even the spill has runned out the oil rigs still give you resorce for unitsd and buildings? They are not disappear from map, aren't they?