Answer:
Step-by-step explanation:
Contrary to the term “oil pool,” oil does not collect in pools underground. It floats upward on ground water (usually saline) until a trap blocks it.
Light blue is water, dark gray is oil, light gray is natural gas. The top row are structural traps, formed by movement of the rocks. The bottom row are stratigraphic traps, where some inherent feature of the sedimentary rocks themselves traps oil.
All the evidence points to the precursors of petroleum being marine algae (not dinosaurs), so it forms in sedimentary rocks. It can rarely migrate into crystalline rocks, if they’re fractured, but sedimentary rocks are porous enough to allow free migration. Folds are one of the most important kinds of traps.