Ultra Low Sulfur Diesel (ULSD) contains 15 ppm sulfur or less, and since 2010, virtually all on-road diesel in the U.S. meets this standard. Modern trucks rely on emissions-control systems like DPF and SCR, making proper ULSD use and clean fuel system maintenance critical. This guide explains what ULSD is, how it works, and how carriers can maintain their trucks properly, especially for pre-2007 engines that require extra attention with ULSD's lower lubricity.
Key takeaways:
- All on-road diesel is ULSD - required by law since 2010 at ≤15 ppm sulfur for highway use.
- ULSD enables modern emissions equipment - DPF, SCR, and EGR systems need low-sulfur fuel to work properly.
- Lower lubricity requires attention - ULSD has less natural lubrication than older diesel, especially important for pre-2007 engines.
- Contamination risks increased - water and microbial growth happen faster without sulfur's natural preservative properties.
- Proper maintenance protects your investment - fuel handling, filtration, and tank hygiene prevent expensive injector and after-treatment problems.
What is ultra low sulfur diesel (ULSD)?
ULSD refers to diesel with sulfur content no greater than 15 parts per million (ppm). This represents a dramatic reduction compared with older diesel, which historically could contain up to 5,000 ppm sulfur before regulations took effect.
For on-road highway trucks in the U.S., ULSD has been required nationwide since 2010. The change wasn't just about cleaner air, it was necessary to make modern emissions-control systems like DPF, SCR, and EGR practical and reliable on commercial trucks.
Why ULSD replaced older diesel
Earlier diesel (sometimes called "low sulfur diesel" at ~500 ppm) was first introduced in 1993 to reduce emissions compared with high-sulfur diesel. To fully enable advanced after-treatment systems, which are sulfur-sensitive, the sulfur content was lowered to 15 ppm, creating ULSD.
The shift cut sulfur-related emissions dramatically while allowing newer engines to meet stricter environmental standards. Without ULSD, the DPF and SCR systems on modern trucks would fail quickly, costing you thousands in repairs. These systems also require diesel exhaust fluid to break down harmful NOx emissions and keep your after-treatment running properly.
Benefits of ULSD for truckers
ULSD delivers real advantages for your operation:
- Cleaner emissions and compliance with EPA requirements
- Compatible with all modern diesel engines and emissions-control systems
- Protects expensive after-treatment components from sulfur damage
- Significantly reduced particulate, sulfur-oxide, and NOx emissions compared with older high-sulfur diesel
Trade-offs truckers need to know
ULSD isn't perfect. The sulfur reduction process also removes compounds that provide natural lubrication:
- Lower natural lubricity compared with high-sulfur or low-sulfur diesel
- More vulnerable to water-related issues when stored or handled improperly
- Increased risk of microbial contamination without sulfur's preservative effect
- Potentially shorter fuel-filter life when fuel quality is poor or with older injection systems
These fuel quality issues add to the ongoing trucking challenges carriers face daily, making proper fuel management even more critical.
How to use ULSD properly to protect your engine
With ULSD, fuel quality and handling become just as important as fuel grade. Given reduced lubricity and increased sensitivity to contamination, carriers must adopt vigilant maintenance and fueling practices.
Use high-quality fuel additives when needed
Especially on older trucks (pre-2007 or older fuel-injection systems), using lubricity additives helps compensate for reduced natural lubrication in ULSD.
In cold climates or winter conditions, anti-gelling additives may be necessary to prevent wax-related fuel gelling or clouding. Cold-weather operators should also pay attention to winter blend diesel fuel availability, which is formulated specifically to prevent gelling in freezing temperatures. Consider additives that also help deter water accumulation or microbial growth when fuel might sit for extended periods, such as in bulk tanks or low-turnover stations.
Maintain fuel filters regularly
Replace fuel filters on the OEM schedule, or sooner if you suspect poor-quality diesel. ULSD's lower lubricity and greater sensitivity to contaminants can accelerate filter clogging.
Monitor for black residue, sludge, water separation, or other signs of contamination like microbes, water, or dirt. In humid or wet operating environments, inspect filters more frequently.
Keep your fuel tanks clean and dry
Drain water separators routinely, weekly is recommended for bulk storage or infrequently used tanks. Avoid fuel from low-turnover stations where fuel may sit longer and risk water ingress or microbial contamination.
In cold weather, keep tanks at least three-quarters full to reduce condensation risk. Avoid large empty volumes that allow air and water contact inside the tank.
Watch your DPF & SCR health
While ULSD reduces particulate and sulfur-related emissions, poor-quality diesel (water, microbes, sediments) can still cause frequent regenerations or catalyst stress.
Be alert for warning signs:
- Loss of power under load
- Increased regeneration frequency
- Reduced fuel economy
- Rough idling
- Injector issues
If problems arise, check fuel source, filters, and water separators. Consider adding additives or improving fueling practices before blaming emissions system components.
Use reputable fuel stations + fuel-management practices
Use stations with high diesel turnover, busy truck stops and known distributor networks are more likely to have clean, fresh ULSD. Avoid rural, off-grid, or low-volume pumps when possible, especially for bulk fueling or long-haul trucks. While price matters when you're looking for the cheapest diesel fuel, quality should never be sacrificed for savings.
For fleets with bulk storage, track fuel batches, turnover, and water content. Maintain regular cleaning and filtration protocols to ensure fuel quality.
ULSD vs. other diesel types
Different diesel types have varying properties that affect your truck's performance and compliance. The weight of diesel varies slightly by type and temperature, which impacts load calculations and fuel tank capacity planning.
Important clarifications
"#2 Diesel" refers to diesel grade (distillation range and volatility), not sulfur content. Nearly all #2 diesel sold today is ULSD (15 ppm) under regulations. The grade affects cold-weather performance, not emissions compliance.
Off-road/dyed/red diesel in many states now also meets ULSD sulfur limits, but dye and tax status make it illegal for highway use. Using dyed diesel on public roads carries steep fines and penalties, even when sulfur content meets ULSD standards.
Biodiesel blends must legally meet ULSD sulfur standards for on-road use. Higher biodiesel percentages (B20 and above) may require stricter cold-weather care and can affect DPF regeneration frequency.
Signs you may be using poor-quality ULSD
If you observe any of the following in your truck or fleet, suspect fuel-quality or contamination issues:
- Frequent DPF regenerations or overactive after-treatment cycles
- Hard starts, rough idle, or injector hesitation (especially under load)
- Loss of power under load or reduced fuel economy
- Rapid or repeated clogging of fuel filters
- Water found in separators or visible fuel-water separation
- Sludge, black residue, or microbial growth in the tank or filter housing
If you're seeing these symptoms, check your fuel source. Consider switching to higher-turnover stations, adding lubricity or water-control additives, draining separators more frequently, or replacing filters earlier than scheduled.
Best practices for storing & handling ULSD (for carriers & fleets)
Proper handling and storage of ULSD matters because the sulfur reduction that makes ULSD "clean" also makes it more vulnerable to contamination, water ingress, and microbial growth.
Recommended practices:
- Use high-quality ULSD from reputable, high-turnover fuel stations (especially for fleet or bulk fueling)
- Add lubricity and anti-gelling additives when needed, especially for older engines or cold-weather operations
- Drain water separators routinely, inspect for water or sediment, never let water accumulate
- Keep tanks mostly full (three-quarters or more) during storage to limit air and water condensation
- Perform regular tank inspections, test for water, microbial growth, and fuel quality, treat with biocide if microbes are detected
- Maintain clean, properly functioning filtration and fuel-delivery systems (fuel filters, water separators, tank vents)
- Keep records of fuel sourcing, tank filling dates, additive use, filter changes, and maintenance for troubleshooting and compliance
FAQs about ultra low sulfur diesel
What is ultra low sulfur diesel fuel?
ULSD is diesel fuel with sulfur content reduced to 15 ppm or less, the standard for virtually all on-road diesel fuel in the U.S. since 2010.
Is off-road diesel ultra-low sulfur?
In most regions, off-road (dyed/red) diesel now also meets the ULSD sulfur standard (≤15 ppm). However, it is dyed for taxation and legal-use purposes and is never legal for highway use. Using dyed diesel on public roads carries significant fines regardless of sulfur content.
Is Diesel #2 the same as ultra low sulfur diesel?
Not necessarily. "#2" denotes the diesel grade (relating to energy content and volatility), not sulfur content. However, nearly all #2 diesel sold in the U.S. today meets the ULSD sulfur specification of ≤15 ppm.
Do all gas stations have ultra low sulfur diesel?
For on-road/highway diesel, yes. Since 2010, all legally sold on-road diesel must be ULSD (≤15 ppm sulfur). For off-road/red-dyed diesel, sulfur content may vary by state or supply, but many supplies now meet ULSD standards. Always check pump labeling and local regulations before use.
Can older trucks run on ULSD?
Yes, but older fuel-injection systems may be more sensitive to lower lubricity. Using lubricity additives and maintaining filters and fuel systems becomes more important for pre-2007 trucks.
Can ULSD cause fuel system wear?
Only if fuel quality is poor or storage and fuel handling is negligent. With good maintenance, clean fuel sources, and proper additives, ULSD is safe and compliant for all diesel engines.
What this means for carriers & fleets
For modern diesel trucks (post-2007 especially), ULSD is required, making fuel-grade decisions easier but elevating the importance of fuel quality and maintenance.
Managing fuel storage, filtration, water separation, and tank hygiene is critical. Supplying clean, properly treated ULSD prevents injector wear, DPF and after-treatment problems, and unplanned downtime.
For older trucks or legacy engines, using ULSD with proper additives and maintenance remains viable, though more attention is required to lubricity and fuel-system care.
Choosing fueling partners carefully (high-turnover stations, reputable supply networks) or using fuel card networks like the OTR Fuel Card that track fuel quality helps ensure consistency and reduce contamination risk.
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