Fill your bottle (or bottles) just over half way full with vegetable oil, then fill with water, leaving about an inch of space at the top.
Add 8-12 drops of food coloring to your bottles.
Place your bottles on a paper plate, just in case to catch any drips! Then add ½ an Alka-Seltzer tablet and watch the bubbles of water rise through the oil (this is the fun part)! After the bubbles have stopped you can add more Alka-Seltzer and keep watching the bubbles rise until your kids are sick of it!
Once the fun is over, we sealed our "lamps" tight and I let the kids proudly display them in the back yard :).
Notes
Make sure you tape around the lids so littler kids can't get them open and spill them anywhere!