I'm not a geologist either, but after I learned how oil, and natural gas forms (basically by living creatures dying then sinking to the bottom of a large body of water, then covered by sediment) it seems to me that it must be very common. (As long as the planet has water, life, sediment and internal heat - which is pretty basic to maintain complex life.) What makes me wonder though, is how short the time period is, in which all of the economically accessible resources can be depleted (putting climate change aside for a moment). Is it 150 or 200 years? What is that in a lifetime of a planet being 4.5 billion years old? That would reduce the chance of meeting an actual high-tech civilization to 1 : 30 000 000... So out of every 30 million exactly Earth like, habitable, planet only 1 is in the process of burning through its fossil fuel reserves... only to collapse within a couple of decades... That chance is so low that I came to believe that we are the only high tech civilization in the Milky Way at the moment. There might be plenty of 'primitive' (or shall I say sustainable?) life forms out there, some even more intelligent, and certainly more wise than us... Some of them even pondering the same question...