Here's a breakdown:
* Source Rocks: These rocks are rich in organic matter (like ancient plankton and algae) that, over millions of years, get buried under layers of sediment and transform into hydrocarbons (like crude oil and natural gas). Common source rocks include shale, limestone, and dolomite.
* Reservoir Rocks: Once formed, the oil and gas migrate from the source rock and accumulate in porous and permeable rocks called reservoir rocks. These rocks act as a "trap" for the oil and gas. Common reservoir rocks include sandstone, limestone, and fractured shale.
* Cap Rocks: To prevent the oil and gas from escaping, there needs to be an impermeable layer of rock called a cap rock (like shale or salt) that seals the reservoir rock.
So, while you don't directly "find" crude oil in the source rock, it's where the oil originates. The source rock acts as the birthplace of oil, while the reservoir rock acts as the storage container.