Minecraft wiki entry for Mining, associated text: So we reach the crux of the argument; tunnel spacing. In the traditional "efficient" mining methods, tunnels are spaced close together in order to "observe" the maximum number of blocks possible, therefore removing all of the ore from an area. So, let's consider a spacing of 1; that is one tunnel separated by one block from another tunnel. During the digging of the first tunnel, several ore bodies are encountered. This tunnel has a high efficiency (in fact, the maximum efficiency possible, as we shall see later). The second tunnel has a very low efficiency because almost all of the ore bodies it encounters have already been removed by the first tunnel. This causes the efficiency of the mining operation to plummet. A spacing of 1 is incredibly inefficient. Now we move to a spacing of 2. This is a spacing that a lot of people use because it leads to 100% observed blocks in a single layer. However, with a spacing of 2, the second tunnel still encounters several ore bodies that have already been removed, so it is also quite inefficient. We can go on like this; as long as the second tunnel has a chance of encountering ore bodies which have already been removed by the adjacent tunnel, it will have a less than maximum efficiency. It follows that the most efficient way to mine is to place the second tunnel far enough away from the adjacent tunnel that there is no chance of encountering ores that have already been removed.