The phrase "strike oil" refers to discovering a valuable resource or finding great success. There are several synonyms for this expression, including "hit the jackpot," "strike gold," "hit pay dirt," and "make a killing." All these expressions convey the same idea of having a significant breakthrough or achieving a considerable amount of success. For example, hitting the jackpot implies that one has had an unexpected windfall of good fortune. Likewise, striking gold and hitting pay dirt both reference uncovering a valuable find after a lot of hard work and effort. Making a killing can mean to make a lot of money or to have a significant win in any area of life. These synonyms reflect the varied contexts in which the phrase "strike oil" can be used.