Here's why:

* Formation: Oil is formed over millions of years from the remains of tiny marine organisms (plankton and algae) that died and settled to the bottom of the ocean. These organic materials were buried under layers of sediment, and as pressure and heat increased, they transformed into hydrocarbons (oil and natural gas).

* Porosity and Permeability: Sedimentary rocks, especially those formed from sand and silt, have a porous structure (spaces within the rock) and permeability (ability for fluids to flow through the rock). This allows oil and natural gas to migrate and accumulate within these formations.

* Source, Reservoir, and Cap Rock: Oil deposits are typically found in three key rock types:

* Source Rock: Where the oil was originally formed. These are usually rich in organic matter and can be shale or limestone.

* Reservoir Rock: Where the oil is stored. These are usually porous and permeable rocks like sandstone, limestone, or fractured shale.

* Cap Rock: A layer of impermeable rock (like shale or salt) that traps the oil in the reservoir rock, preventing it from escaping.

Common types of sedimentary rocks where oil deposits are found:

* Sandstone: Often a primary reservoir rock due to its high porosity and permeability.

* Limestone: Can be a reservoir rock, especially if it has been fractured or has cavities.

* Shale: Often acts as both the source rock (containing the organic matter) and a cap rock (preventing oil migration).

It's important to note: While oil deposits are typically found in sedimentary rocks, they can also be found in metamorphic and igneous rocks under specific geological conditions. However, these are less common occurrences.