If you work anywhere in the petroleum, fuel distribution, or industrial dye sector, chances are you have come across Red 164 — or at least seen its effects without realising it. That distinctive red tint in off-road diesel? That is Solvent Red 164 (CAS No. 92257-31-3) at work. It is one of those quietly essential chemicals that most people never think about, yet it plays a massive role in fuel tax enforcement, industrial colour-coding, and even manufacturing of petroleum products.
In this guide, we are going to break down exactly what Red 164 is, why it matters, where it is used, and how it compares with similar dyes. Whether you are a procurement manager sourcing fuel dyes, an engineer specifying colourants for lubricants, or simply curious about the chemistry behind coloured fuels, this article is for you.
What Exactly Is Red 164?
Red 164, formally known as C.I. Solvent Red 164, is a synthetic diazo dye belonging to the azo chemical family. The molecular formula is C₃₁H₃₄N₄O, giving it a molecular weight of approximately 478.63 g/mol.
In practical terms, Red 164 is a deep bluish-red, oil-soluble dye that dissolves readily in hydrocarbon solvents and petroleum products. It was specifically developed as a higher-solubility alternative to Solvent Red 26 — the original reference standard used in the United States for fuel marking purposes.
The key structural difference? Red 164 contains additional alkyl (hydrocarbon) chains compared to Solvent Red 26. These chains do not change the colour — the visible absorption spectrum is virtually identical — but they dramatically improve solubility in diesel and burner fuels. That is precisely why the industry shifted to Red 164 for real-world fuel dyeing applications.
Key Chemical Properties of Red 164 (CAS 92257-31-3.)
The table below summarises the essential chemical and physical properties of Red 164 (CAS 92257-31-3):
| Property | Details |
| C.I. Name | Solvent Red 164 |
| CAS Number | 92257-31-3 (liquid formulations) |
| Chemical Class | Diazo (Double Azo) |
| Molecular Formula | C₃₁H₃₄N₄O |
| Molecular Weight | 478.63 g/mol |
| Hue | Bluish Red |
| Solubility | Oil-soluble; highly miscible in petroleum products |
| Physical Form | Liquid (in solvent); also available as powder |
| Common Solvents | High-flash (HF) solvents, Xylene (XY) |
| Regulatory Standard | ASTM D6258-17 (fuel dye concentration testing) |
| IUPAC Name | 1-[[2,5-dimethyl-4-[(2-methylphenyl)azo]phenyl]azo]-2-naphthol |
These properties make Red 164 ideally suited for applications where the dye must dissolve completely and remain stable without affecting the chemical performance of the host product.
Primary Applications of Red 164
1. Tax-Exempt Fuel Marking (The Biggest Use Case)
This is where Red 164 truly shines — and where it has had the most significant industrial impact. In the United States, federal regulations under 26 CFR 48.4082-1(b) mandate that all tax-exempt diesel fuel must be dyed red using Solvent Red 164 (CAS 92257-31-3). The specific requirement is that the dye concentration must be spectrally equivalent to 3.9 pounds of Solvent Red 26 per 1,000 barrels of fuel (approximately 11.1 mg/L).
Because Red 164 offers superior solubility compared to Solvent Red 26 at a lower cost, it has become the standard dye used by refineries and terminals across North America. The ASTM D6258-17 test method was developed specifically to measure Red 164 concentrations in commercially available diesel fuels using visible spectroscopy.
The concept is straightforward: tax-exempt diesel (used for off-road purposes like agriculture, construction, and heating) is dyed red so that enforcement officers can visually confirm whether a vehicle is using taxed or untaxed fuel. Using dyed fuel in on-road vehicles is illegal and carries heavy penalties.
2. Petroleum Product Colour-Coding
Beyond tax enforcement, Red 164 is widely used by refineries to colour-code different fuel grades and petroleum products. This practice helps prevent mix-ups during storage, transportation, and distribution. Think of it as an industrial safety measure — when you can visually distinguish high-sulphur diesel from low-sulphur diesel, costly cross-contamination errors are far less likely.
3. Industrial and Speciality Applications
Red 164 is also used in colouring lubricants (such as transmission fluid), hydraulic fluids, waxes, greases, candles, printing inks, and certain plastic and polymer formulations. Its oil-soluble nature makes it versatile across any application that requires a stable, vivid red colourant in a non-aqueous system.
Application Overview Table
| Application Sector | Specific Use | Why Red 164 Is Preferred |
| Fuel & Petroleum | Tax-exempt diesel, kerosene, gas oil | High solubility, regulatory compliance, cost effective |
| Lubricants & Fluids | Transmission fluid, hydraulic oil | Complete dissolution, no residue, stable colour, Brand identity |
| Wax & Candles | Paraffin, soy, and gel wax colouring | Excellent wax compatibility, vibrant hue |
| Printing Inks | Oil-based ink formulations | Strong tinting strength, fast dispersion |
| Plastics & Polymers | Mass colouring of PE, PP, and rubber | Thermal stability, even distribution |
Red 164 vs. Solvent Red 26: What Is the Difference?
This is one of the most common questions we encounter. Solvent Red 26 is the certified pure reference standard — it is the benchmark against which Red 164 concentrations are measured. Red 164 is essentially the commercial, field-grade version that has been alkylated (modified with additional hydrocarbon chains) for better real-world performance.
| Parameter | Solvent Red 26 | Red 164 (Solvent Red 164) |
| CAS Number | 85-83-6 | 92257-31-3 |
| Chemical Structure | Base diazo structure | Alkylated variant of SR 26 |
| Solubility in Diesel | Moderate | High (significantly better) |
| Cost | Higher (certified pure) | Lower (commercial grade) |
| Role | Reference standard for testing | Field-use dye for fuel marking |
| Visible Spectrum | Baseline standard | Virtually identical to SR 26 |
| Availability | Limited (lab/calibration use) | Widely available commercially |
In short, if Solvent Red 26 is the gold standard sitting in the laboratory, Red 164 is the workhorse doing the heavy lifting at every refinery and fuel terminal.
Case Study: How a Mid-Size Fuel Distributor Solved Compliance Challenges with Red 164
Background: A regional fuel distributor operating across three states in the American Midwest was flagged during a routine IRS audit for inconsistent dye concentrations in their tax-exempt diesel. Their existing dyeing process relied on manual injection of a lower-solubility red dye at each terminal, and testing revealed that concentrations varied by as much as 40% between batches — some falling below the mandated 11.1 mg/L spectral equivalency.
The Problem: Inconsistent dye dispersion was causing uneven colour across storage tanks, raising compliance risks. The distributor faced potential penalties and needed a reliable, uniform dyeing solution that could work across their existing injection infrastructure.
The Solution: After evaluating several options, the distributor switched to a high-flash Solvent Red 164 (CAS 92257-31-3) liquid formulation supplied by a manufacturer with established expertise in petroleum dyes. The new formulation offered complete miscibility in diesel without requiring pre-mixing or heated injection, and it maintained stable concentration even across large-volume storage tanks.
Results:
| Metric | Before (Old Dye) | After (Red 164 Switch) |
| Dye Concentration Variance | ±40% | ±3% |
| ASTM D6258 Compliance Rate | 72% | 99.6% |
| Injection System Modifications | N/A | None required |
| Annual Dye Cost | Baseline | ~18% reduction |
| Audit Flags (12-month period) | 3 | 0 |
Key Takeaway: The switch to a quality-assured Red 164 formulation not only brought the distributor into full regulatory compliance but also reduced their overall dye costs. This case illustrates why sourcing Red 164 from an experienced, ISO-certified manufacturer — one that ensures batch-to-batch consistency and zero insoluble residue — can make a tangible difference to operations.
What to Look for When Sourcing Red 164
Not all Red 164 products are created equal. Since the CAS 92257-31-3 designation covers a range of alkylated variants, the exact composition can vary from manufacturer to manufacturer and lot to lot. Here are the qualities that matter most when evaluating a supplier:
Purity and consistency: The dye should be free of insoluble impurities that could clog injection systems or create sediment in fuel tanks. Look for suppliers who perform rigorous quality testing on every batch.
Complete miscibility: Red 164 should dissolve fully in diesel, kerosene, and other petroleum products without cloudiness or phase separation.
Regulatory compliance: Ensure the product meets ASTM D6258-17 requirements and any local fuel-marking regulations applicable to your market.
ISO certification: Manufacturers with ISO 9001:2015, ISO 14001:2015, and ISO 45001:2018 certifications demonstrate commitment to quality, environmental responsibility, and worker safety.
Custom formulations: Some applications require specific solvent bases (high-flash, xylene, toluene) or tailored concentrations. An experienced manufacturer will offer flexibility here.
Anar Chemicals LLP (anarchem.com) is one such manufacturer — an ISO 9001:2015, ISO 14001:2015 & ISO 45001:2018 certified company with over four decades of experience in dyes and speciality chemicals. They produce Red 164 (CAS 92257-31-3) in both high-flash and xylene solvent bases, alongside a comprehensive range of other petroleum dyes. You can explore their full Liquid Petroleum or Fuel Dyes product range on their site.
Frequently Asked Questions About Red 164
Q: What is Red 164 used for?
Red 164, or Solvent Red 164 (CAS 92257-31-3), is primarily used to dye tax-exempt diesel fuel red for regulatory enforcement purposes. It is also used in colouring lubricants, hydraulic fluids, printing inks, waxes, candles, and certain plastics.
Q: Is Red 164 the same as Solvent Red 26?
Not exactly. Red 164 is an alkylated version of Solvent Red 26, meaning it has additional hydrocarbon chains to improve its solubility in diesel fuel. Both have virtually identical visible absorption spectra, but Red 164 is the commercial-grade dye used in the field, while Solvent Red 26 serves as the certified laboratory reference standard.
Q: What is the CAS number for Red 164?
The most commonly cited CAS number for Solvent Red 164 is 92257-31-3. Some commercial liquid formulations may also be listed under CAS 92257-31-3, depending on the specific alkylated variant and solvent base used.
Q: Why is diesel fuel dyed red?
Diesel fuel is dyed red to indicate that it is tax-exempt — meaning it is intended for off-road uses such as agriculture, construction, or heating. This visual marker allows enforcement agencies to quickly identify whether a vehicle is illegally using untaxed fuel on public roads.
Q: What is the required concentration of Red 164 in diesel fuel?
In the United States, federal regulations require that tax-exempt diesel contain Red 164 at a concentration spectrally equivalent to 3.9 pounds of Solvent Red 26 per 1,000 barrels, which translates to approximately 11.1 mg/L. This is measured using ASTM D6258-17 methodology.
Q: Does Red 164 affect fuel performance?
No. Solvent Red 164 (CAS 92257-31-3) is chemically inert in hydrocarbon systems. When added at the mandated concentrations (parts-per-million levels), it does not alter the combustion characteristics, cetane number, or overall performance of diesel fuel.
Q: Where can I buy high-quality Red 164?
Red 164 is available from speciality chemical manufacturers such as Anar Chemicals LLP (anarchem.com), which produces petroleum-grade Solvent Red 164 in high-flash and xylene solvent bases. Look for ISO-certified manufacturers who guarantee impurity-free products and batch-to-batch consistency.
Q: Is Solvent Red 164 safe to handle?
Like most industrial dyes, Red 164 should be handled with standard safety precautions — protective gloves, eye protection, and adequate ventilation. Always refer to the manufacturer’s Safety Data Sheet (SDS/MSDS) for specific handling, storage, and disposal guidelines.