What's the priority - cleaning up the mess, or stopping the leak? The former will depend on the floor surface. Worst-case scenario is that it's carpet, in which case if it's soaked in, there's little you can do. Blotting with absorbent paper may help, then shampooing might rescue it to some extent, but heating oil tends to be mucky stuff. Shut off the oil feed either at the appliance or the tank and call a plumber or heating engineer. If you've a stone or tiled floor, you're laughing. A few moppings out with detergent will get rid of it. Lino, similarly, if the oil's not got down into the joins. If it's a laminate floor it may buckle with the swelling that the oil soaking into it can cause. I do hope you can rescue the situation.