Yes, the subway has no special restrictions on liquids, and edible oil is not contraband. Take the regulations of Beijing subway as an example:

It is forbidden to carry inflammable, explosive, toxic, corrosive, radioactive and lethal dangerous goods (such as detonators, explosives, firecrackers, gasoline, diesel oil, kerosene, paint, calcium carbide, liquefied gas, controlled knives, various acids, etc.) and other items that endanger the safety of the public.