I wouldn't be too worried about liquid fuels. The recovery rate from oil wells is only about 5%. It's just a matter of time before some smart engineer works out how to improve on that and tap back into old drilling areas like they've done for natural gas. There's at least 200 years of supply for natural gas and it's only a matter of time before there is a push to get more refueling stations to carry natural gas and the carmakers won't be far behind. We've barely touched shale oils, which are now viable. Nor have we touched methane clathrates yet. The technology to tap into that area will be coming. A conservative estimate on methane clathrate deposits is twice the total of all other carbon-based fuels (coal, natural gas, oil, etc) combined.