Hi Ben,
Do not use motor oil and fire!!!, that is not something you want to do anywhere, let alone in a garden plot. Burning is an option for stumps (albeit a bad one in my opinion) but only after they are out of the ground and dried.
The following lead my list:
1. Ladder jack (or
tractor jack as some call them) with a strap to the trunk of tree 200 mm dia an smaller. You can pop them right out of the ground. On larger trees you can do it one side at a time.
2. tripod and chain hoist-block and tackel to rip from the ground (requires some special skill sets and tools)
3. tractor with back hoe (again special skill sets and tools)
4. Rent a stump grinder or hire someone with it to remove the stump.
5. Dig in up and remove in pieces.
6. Cut flush, drill with 25 mm (1") auger bit, and cover with dirt, plant as usual. This is a natural Hugalculture start.
Those are the best top choices that I have come across and used, (not in order of importance.)