A dry well, also known as a dry hole, can still have oil in it, however only in small amounts. A well is considered dry if it produces no oil at all, or simply not enough oil for the well to be commercially viable.
During the process of oil exploration, wells are drilled in areas suspected of having oil. Many of these wells are known as dry wells, as while they may have gas or oil, it is uneconomical to extract it. A well which was previously profitable may also become dry when so much oil or gas has been extracted, that what little remains is too difficult and expensive to extract.