The phrase "lot of oil" refers to a large amount or supply of oil. It can be used in various contexts, such as referring to the amount of oil that is extracted from wells, the amount of oil that is used in an industrial process, or the amount of oil that is available in a storage facility. The phrase can also be used in a more general sense to describe someone who has "a lot of oil" in their engine or machine, meaning that they have enough oil to keep the machine running smoothly.