The Bronze Oil Lamp is the eighty-fourth treasure that can be found in Uncharted 2: Among Thieves.
The Bronze Oil Lamp is found in Chapter 23 - Reunion. When the Heavy Weapons Troops and all the other soldiers here are defeated, you can easily grab another treasure. Thankfully, this treasure's location is actually en route to our next destination, so you can do it all at once. Run back towards the origin-point of this area, where you initially dropped in once you went through the previous door. Nearby should be a green and yellow ladder scaling upward into the half-wrecked building adjacent to you. Climb on up to the topmost floor and move rightward and then forward. The path will eventually drop off. It's at this point that you should look up and to your left. While you might have spotted this treasure from below, at the bottom of the courtyard, here is where you must acquire it. Use a firearm to knock the treasure from its perch, and then pick it up once it's fallen.