Dyed diesel is ordinary diesel fuel with red dye added, so a red tint is the clearest visual clue. Check the pump or storage labels and the fuel’s paperwork to corroborate what it is. Color alone does not establish the fuel’s tax status, sulfur content, quality, or whether using it is legal where you are.
How to identify dyed diesel
Look for a red tint in a fuel sample. North Carolina’s Department of Revenue defines dyed diesel as regular diesel fuel with red dye added (Guide for Dyed Diesel Use). A red appearance is a clue, not a complete identification test: the sources do not establish that every sample will look the same or provide a consumer test that conclusively distinguishes dyed from undyed fuel.
Check the context as well as the color:
- At the pump or delivery point: Look for a notice identifying the fuel as dyed and restricting it to nontaxable use.
- On the tank or container: Check for a label indicating dyed fuel or off-road use.
- In the paperwork: Review the invoice, bill of lading, or other fuel records. IRS guidance requires a conspicuous dyed-fuel notice in specified sales and delivery contexts; Illinois also describes notices for storage and sales records.
The IRS notice is: “DYED DIESEL FUEL, NONTAXABLE USE ONLY, PENALTY FOR TAXABLE USE.” Its application depends on the sales or delivery context described in IRS Publication 510. Illinois’s state-specific notice requirements are described in its Dyed Diesel General Information and Requirements.
If the fuel’s identity affects a legal or operational decision and its color or records are unclear, contact the supplier or the fuel-tax authority for your jurisdiction. Do not rely on an improvised test to settle the question.
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What red dye tells you—and what it does not
Red dye identifies fuel designated for nontaxable or non-highway use under applicable rules. North Carolina and Montana describe dyed diesel as intended for off-road use (North Carolina guidance; Montana Department of Transportation guidance).
The color does not establish sulfur content, engine compatibility, or overall fuel quality. In a 2020 final rule, the EPA said red dye no longer provided meaningful additional assurance of compliance with ultra-low-sulfur diesel standards as other distillate fuels became subject to the same 15 ppm sulfur standard. The rule removed EPA’s requirement that motor-vehicle diesel be free of visible red dye, while noting the separate federal tax-law dye requirement for qualifying tax-exempt fuel (EPA final rule). Do not use color as a substitute for a fuel specification or analysis.
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- LAB TESTING NOT INCLUDED — This purchase is the life-safety FOI diesel fuel sample collection and shipping kit. It provides the materials and documentation needed to properly collect in continuity and submit a diesel fuel sample to a laboratory. Laboratory analysis and testing fees are purchased separately.
- FIRST STEP IN THE CONTINUITY WORKFLOW — The standby sample kit establishes the prepared starting point for an FOI fuel-quality event. Having the correct sampling materials, documentation, and shipping pathway, stand-by ready, allows the continuity workflow and chain of custody to begin at the time the sample is taken rather than after materials must be sourced.
- ESTABLISHES DOCUMENTED SAMPLE CUSTODY — The included Sample Information Form (SIF), container, secondary containment, absorbent materials, isolation packaging, and instructions support a documented chain of custody, tracking the sample from the source thru final record.
- WHAT'S INCLUDED — A engineered life-safety diesel-compatible sample container, secondary containment, absorbent material, isolation packaging, shipping carton, Sample Information Form, and collection/shipping instructions for shipping a diesel sample safely.
- LABORATORY ANALYSIS AVAILABLE SEPARATELY — After collection, the sample may be submitted to FOI Laboratories for the appropriate ASTM D975 / NFPA 110 fuel-quality testing package. Laboratory testing is not included with the purchase of this kit.
Dyed diesel and undyed diesel compared
| What to check | Dyed diesel | Undyed diesel |
|---|---|---|
| Visible clue | Red dye is deliberately added; the fuel may show a red tint. | Does not have the deliberately added red dye. |
| Labels and records | Look for dyed-fuel notices on applicable pumps, tanks, delivery documents, or sales records. | Check the pump label and records for the fuel’s identity and intended use. |
| Typical stated use | Designated for nontaxable or off-road use under applicable rules. | Use and tax treatment depend on the product and jurisdiction; undyed color alone does not prove either. |
| What color establishes | It may indicate dye is present, but does not establish sulfur level, quality, or legal eligibility for a particular use. | Absence of visible red dye does not establish sulfur level, quality, or legal eligibility for a particular use. |
Why rules depend on where and how the fuel is used
Federal rules address dyeing, notices, and penalties for misuse or alteration; state rules can impose additional restrictions and penalties. The IRS’s Publication 510 (December 2025 edition) describes federal requirements. It is not a complete guide to every state’s road-use rules or exceptions.
For example, Illinois says tax-paid, undyed diesel is the fuel allowed in ordinary tanks of specified highway-registered vehicles and recreational watercraft in that state, and sets out state enforcement penalties in its requirements guidance. North Carolina also states its own off-road-use rules and penalties in its guidance. These examples should not be treated as nationwide rules. Check current federal and local requirements before using dyed fuel in a vehicle or equipment.
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When appearance and records are inconclusive
The reviewed official guidance does not establish a consumer test kit or simple field protocol that conclusively identifies dyed fuel. Illinois describes sampling as part of authorized enforcement inspections (Dyed Diesel Fuel Enforcement Program), not as a consumer test. If a definitive identification is needed, ask the supplier or relevant fuel-tax authority how to proceed.
Quick Recap
Best Value
- OTC's 6750 Diesel Fuel Hydrometer allows technicians to quickly troubleshoot engine performance problems and measure #1 and #2 grade diesel fuel quality
- Hydrometer measurements are given as an American Petroleum Institute (API) gravity reading when testing diesel fuel composition and combustion characteristics
- Fuel is drawn into the hydrometer tube which then floats the internal bulb float; Internal float contains a thermometer that is used to compensate the API reading for the highest accuracy
- Hydrometer Scale: 30 to 110; Correction Scale: +2.5 to -5.0; applications include #1 and #2 grade diesel fuels
- Similar to OE tool number J-38641-D; Instructions included
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- Reliable Results, Every Time: Trusted by professionals for routine maintenance and preemptive quality checks.
- Portable & Cost-Effective: Compact kit for on-the-go testing—save time and money by catching issues early.
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