|Oil well value|
|Required for||Units: Battleship, Landship, Tank, Panzer, Triplane, Fighter, Great war bomber, Bomber, B17|
Late-game strategic resource. Used by most of the powerful late industrial-early modern era units.
Oil is the first late-game strategic resource (revealed by the Biology tech), and is quite unique for a number of reasons. First, it is the only strategic resource found on both land and sea. Second, it is the only resource which requires two unique new improvements to access: the Oil Well for land-based sources, and the Offshore Platform for sea-based ones. Finally, its sources are in weird locations - deserts, snow, and tundra terrain or anywhere on coastal tiles. Of these, Oil is most often found in deserts, which gives desert-based civilizations a unique advantage - they can be all but sure that they will reveal multiple sources already within their territory. Otherwise, be ready to expand immediately after you reveal the Oil sources.
The Oil resource doesn't provide a big Production bonus per se (only +1), but the improvements add a whopping +3 Production bonus, which makes the tile really productive. Sea-based sources of Oil are even more useful, because of the additional bonus the Lighthouse and the Seaport provide (+2 Production and +1 Gold, apart from the Offshore Platform's own bonus).
Oil is used for most early late-game machines on land, sea and air, such as armored units and airplanes, so militaristic civilizations should make sure they have plenty of Oil to continue their wars.
Oil is a liquid fuel found in large and small deposits across the world. Although occasionally used by some civilizations as far back as four thousand years ago to create asphalt or naptha or burned as a light source, modern use can be traced back to 1857 when the first modern refinery was constructed in Alsace, France. At about the same time wells were being drilled across Europe and in North America. By the early 20th century oil was in great demand, largely due to its use in internal combustion engines as used by ships, planes, and automobiles. Today much of international politics is driven by growing tension between those who have abundant sources of oil, and those who do not. Remember that oil is a strategic resource, and thus it is consumed as you construct the associated units and buildings.