Oil can work as a form of pitch and asphalt that can be harvested and used for waterproofing wood, provided people start building warships and such out of wood materials and such (most effective for below water level; can also add difficulty in building through aquifers), and additionally, harvesting and pooling oil into buckets or minecarts, set them on fire, and dumping them over your fortress walls and on top of sieges and ambushers to give them a "fair warning" about your fort.
Provided lighting gets implemented a little more past adventure mode, kerosene production can be used for cave exploration and laying torches/lanterns all over the place to improve the atmosphere or lighting of the fortress interior. Naturally, for fortress mode, they would add to the aesthetics of the fort, but as an added bonus, they can also fend off pests/vermin.
To make a lantern (classic genie lamp style), you'd require 1 metal bar, 1/7 (or bucket) processed oil/kerosene, and 1 fiber rope. Glass lanterns would include 1 glass block, and can be placed/built, as well as carried; whereas the other is more like a finished good rather than furniture. Naturally, they will eventually need to be reloaded with more oil or fiber rope to keep them working/lit indefinitely. A bit of simple maintainence, especially where long lasting forts are concerned. Such a task could be assigned to Furniture hauling job.
For torches, they'd be a wood log and a small stack of cloth, (1 log (or a stack of bones), 2 cloth rolls, 1 bucket of pitch oil = 10 torches). Can be carried and placed, but aren't as effective as lanterns. Alternatively, skulls can be used for making lanterns or skull candle holders. As good quality decoration as a totem. Alternatively, (5) (bees)wax candle + Totem = Skull chandelier/Candle-post.