Oil recovery techniques are methods used to extract crude oil from underground reservoirs. The primary techniques include primary recovery, which relies on natural pressure to push oil to the surface, and secondary recovery, which involves injecting water or gas to maintain pressure and enhance extraction. Tertiary recovery, also known as enhanced oil recovery (EOR), employs advanced methods like thermal recovery, gas injection, or chemical flooding to increase the amount of oil that can be extracted. These techniques help maximize production and improve the efficiency of oil extraction from fields like the North Sea or the Permian Basin.