This light blue paper turns dark blue in the presence of hydrocarbons, particularly gasoline, fuel oil, lubricating oil, etc. It is recommended for the rapid determination of oil contaminations in water and/or soil. To determine oil in water, move the paper back and forth a few times in the test solution. For detection of oil in soil, press the paper firmly against the soil to be tested and rinse it with clear water. With volatile hydrocarbons, the color reaction of the test paper has to be evaluated immediately. Limit of sensitivity: The sensitivity of the test paper is largely dependent on the solubility of the hydrocarbons.