Crude petroleum oil deposits can be found deep in aquatic environments. Simply drill into patches of earth that are leaking oil to collect it.
The black crud is inert and will not harm you in any way. It makes for great fuel and is very dependable.
Can be found at:Edit
Aquatic Planet: 150-250 depth
make sure you have enough HP, repair kit, and repair material (Orichalcum Ore in this case)Oil like vespene,therazene, and amaranthine. It has deposit, so you will see oil in red area in minimap (if you've already upgraded optics). This Oil deposit look like: