This document specifies a test method for the determination of the content of n-butyl phenyl ether (BPE, also known as butoxy-benzene) in gas oils, kerosene, diesel fuel and biodiesel blends. The method uses a two-column gas chromatograph with an FID-type of detector. The application range is 0,1 mg/l to 21,25 mg/l of BPE, with a limit of detection of 0,05 mg/l. NOTE This corresponds to 1 % to 150 % of the average marking level of the ACCUTRACE"! Plus required by Commission Implementing Decision (EU) 2022/197 [1] of 17 January 2022 establishing a common fiscal marker for gas oils and kerosene. The method is found to be applicable to determinations beyond this range or for specific other chemical markers that fall within the distillation temperature range of middle-distillates, but for that no precision has been determined. WARNING The use of this document may involve hazardous materials, operations and equipment. This document does not purport to address all of the safety problems associated with its use. It is the responsibility of the user of this document to establish appropriate safety and health practices and to determine the applicability of regulatory limitations prior to use.