Petroleum products (e.g. gasoline, lubricant oil, fuel oil and organic solvents and diluents) are readily available to everybody. Owing to their physicochemical properties, especially volatility and inflammability, these products are often used in crimes (e.g. arsons) and, furthermore, they could cause contamination of the environment. Examples of determination of potential accelerants in samples collected from places of arson as well as samples contaminating water in a well are presented. Passive adsorption on Tenax TA as a method of isolation of petroleum products from a matrix was used. Identification of adsorbed compounds was carried out using a gas chromatograph (GC) coupled with auto-thermal desorber (ATD) and mass spectrometer (MS).