This practice establishes the standard method of preserving waterborne oil samples from the time of collection to the time of analysis. Information is provided to ensure sample integrity and to avoid contamination and to minimize microbial degradation. This practice is for controlled field or laboratory conditions and specifies thorough preparation of equipment and precise operation. If, however, these details must be compromised in a field emergency, nonstandard simplifications that will minimize or eliminate consequent errors are recommended. This procedure requires the use of the following apparatuses: sample containers, preferably borosilicate glass (plastic and metal are not acceptable ); closures; an explosion-proof refrigerator; and shipping containers (sturdy cartons or wooden boxes). Samples may be of several types, such as tar balls, collected oil, oil-water mixtures, emulsions, and oil and water on collecting devices such as silanized glass cloth, TFE-fluorocarbon polymer, or other materials. Instructions are given for the care of samples to minimize changes due to autoxidation and microbial attack between the time of sampling and the time of testing. Services available for transportation of samples are described as well.