It's land surface area. Some is leased/owned land that may be unutilized, but coal mining surface area on its own approaches the necessary amount of land needed

It's land surface area. Some is leased/owned land that may be unutilized, but coal mining surface area on its own approaches the necessary amount of land needed. Oil rigs may have a small physical footprint by themselves, but they generally have pads cleared off for them and then fields can have multiple pads and access paths. See: https://e360.yale.edu/assets/site/_1500x750_crop_center-center/MidwaySunsetOilFieldCalifornia_MarkRalstonAFPGettyImages_2000.jpg https://e360.yale.edu/assets/site/_1500x750_crop_center-cent... https://www.bloomberg.com/news/articles/2018-10-16/the-permian-oil-boom-is-showing-signs-of-overheating https://www.bloomberg.com/news/articles/2018-10-16/the-permi...