The Oil Platform is an economic building used to gather Oil from oil patches at sea. It is the marine version of the Oil Well and automatically selected when trying to build an Oil Well at sea. Both structures become available in the Industrial Age (along with the resource oil itself) and require Timber and Metal to build. The Oil Platform's stats are almost identical to those of the Oil Well (including hit points and plunder amount), however, the Platform has a slightly higher ramping cost. Ramping cost of Oil Wells and Oil Platforms are linked – building either structure also raises the cost for the other.
Keep in mind, that a nation needs to own at least one Dock and has to have developed Science 1 (Written Word) in order to allow Citizens to embark on transport vessels – otherwise they won't be able to get to the construction site.
Like the Oil Well, the Oil Platform needs to be operated by a citizen and gathers oil at a rate of 35 (per 30 seconds). When a Platform is destroyed or razed, the citizen is automatically ejected from it. The Citizen can also be ejected manually, leaving the structure without function (it still belongs to the nation, however, and blocks the oil patch from enemy access).
The gather rate of oil can be increased by building Refineries, with each Refinery adding 33% to the global base gather rate.