Engine Oil works as a booster for your Machines.
You can make it in the Bio Press by pressing all kinds of seeds.
As a side effect of pressing oil, you will create Biomass which is handy for recharging Golems.
As a side effect of oiling your machines, they will produce Toxic Water which you need to get rid of through the Liquid Depo.
Then you can either store it in barrels or pour it into water flowing out of a map.