Purchase the following materials for your experiment: motor oil, two aquariums, aquatic plants of any type, water pH test strips, aquarium oxygen generators and aquarium soil. Make sure that you purchase the same plants for both aquariums. The aquariums should also be the same size and the oxygen generators should be the same brand and type. Everything must be the same in each of the aquariums except for the variable -- which will be the oil.
Layer aquarium soil at the bottom of your aquariums. Measure the depth of the soil to make sure it is the same depth throughout each aquarium. Place at least 3 to 4 inches to give room for your aquatic plants to grow and spread out. Place your oxygen generators on the side of the tank and hook them to a power source. Plant your aquatic plants and fill the aquarium tanks with water. Test the pH of the water with your strips to make sure it is appropriate for your plants. Use filtered or distilled water to keep the water free from outside influences such as chemicals.
Let your plants grow for a week or so before beginning your experiment. After the week has passed, dump the oil into one of the aquariums. Keep the aquariums away from any young children or animals so they don't get into it and hurt themselves. Watch the way the oil spreads over the following days. Don't add more oil to the water but make sure you add enough so that some of it starts to sink below the surface of the water.
Observe the way the oil begins to act on the plants. Note when it finally comes into contact with the plants and if the plants begin to die or wither away. Pay attention to whether the plants start changing before the oil hits them. Compare these plants to the ones in the aquarium without oil. Monitor the growth and behavior of both sets of plants over a week. Clean the oil out of the tank and remove the plants. Observe how the oil interacted with the plant material.