A kerogen-rich source rock that has been 'cooked' to thermal maturity. So you need lots of organic matter, burial, and time.
A migration pathway from the source to a trapping configuration, and time for this to have happened.
A structural or stratigraphic trap, such as an anticline, and the geological conditions that have preserved it since filling.
A reservoir rock — a porous and permeable rock. Usually this is a sedimentary rock (like sandstone, which there's lots of in Saudi!).