On November 24, 1993, the Internal Revenue Service issued a “Notice of Proposed Rule Making” relating taxation of on-road diesel fuels and policing by means of a dyeing program. Based on the proposed regulation, various qualitative and quantitative methods were developed by two laboratories to identify and determine concentration of various dyes in No. 1 and No. 2 diesel fuels. A simple qualitative method was devised which consists of extracting the dye out of the fuel and identifying dye composition by thin layer chromatography. Quantitative methods were also developed based on spectrophometric evaluation of dyed fuel. The quantitative methods are designed for use with low cost single beam spectrophometers. Independent results based on a nine terminal sampling program are included.