Oil is a very precious resource in the Ark: Survival Evolved. There are many approaches to find oil in Ark. It depends on how much you need, how much time you have, the map you are playing, and how advanced you are in the game. If you don't want cost more time finding, you can Buy ARK Dinos from arkrex.com. Let's introduce the method for you below.

How To Find Oil
At the beginning of the game, when you only need a small amount of oil to make a propellant or turn meat into jerky, the best option to discover oil is to kill trilobites. Trilobites are small marine creatures that fly above the bottom of shallow lakes and rivers. They can be easily mistaken for rocks, however, they are almost always seen in groups. Killing them will produce a handful of oil, but make sure you might have an attack plan: when you kill a trilobite, others in the region will back off, so it will be difficult to kill them effectively.

Once you might have better armor, decent water dinosaurs, and enough courage, another best way to accumulate oil would be to search for black nodes from the riverbed and ocean floor. However, this is a risky approach because many of the most dangerous creatures in the game are lurking inside the water. If you plan to gather oil in this manner, it is recommended that you tame extremely high-speed water mounts. 

As a novice, ichthyosaurs have to be your best choice, since they are very fast as well as simple to tame. However, keep in mind that they have no offensive capabilities. It is also recommended that you consume Lazarus Chowder so as to hold your breath for enough time to mine deeper water.

If sailing will not be what you want, then an alternative for collecting oil would be to search for black nodes over the snow biome. Remember to wear fur to protect yourself from extreme cold. It is also recommended that you bring ankylosaurus in order to mine as soon as possible. If you don't have an ankylosaurus, you can buy ARK Dinos For Sale. In addition, snow also has its own dangers, such as the many dire wolves and Argentine birds that inhabit the area, so underwater nodes may still be your best choice.