Is Ultra-Low Sulfur Diesel (ULSD) Required in Canada and the USA?

If you operate diesel-powered equipment in Canada or the United States-whether it's trucks, generators, or industrial machinery-you’ve probably come across the term ULSD, or Ultra-Low Sulfur Diesel. It’s not just a cleaner fuel; it's also the law. But when exactly did ULSD become mandatory? What does this mean for your diesel engines, particularly when it comes to emergency generators?

LET’S BREAK IT DOWN.

What Is ULSD Fuel?

Ultra-low sulfur diesel (ULSD) is a type of diesel fuel that has a sulfur concentration limited to 15 parts per million or less. Compare that to older low-sulfur diesel (LSD), which could have up to 500 ppm, and you’ll see why it’s called “ultra-low.”

The main reason for this shift? Sulfur contributes heavily to air pollution. When diesel is burned, the sulfur it contains converts into sulfur dioxide, a key contributor to both smog formation and acid rain. Reducing sulfur makes diesel engines cleaner and more compatible with advanced emission systems.

Is ULSD Fuel Mandatory in the USA?

Yes, ULSD has been mandatory in the U.S. since 2010 for almost all on-road and off-road diesel engines. 

Here's how it was phased in:

2006: ULSD required for on-road diesel vehicles like trucks and buses.

2010: All new on-road diesel engines had to be ULSD-compatible with emissions controls (like DPFs and SCR).

2011-2014: There was a gradual transition to ULSD for off-road engines used in construction, agriculture, and industrial machinery.

Since 2014, all diesel fuel sold in the U.S. must be ULSD, except for some special exemptions (like marine or locomotive use, which also faced stricter standards later).

This applies to standby diesel generators too. Even if they’re rarely used, they still fall under fuel regulations unless they qualify for very specific exemptions (which are rare and limited).

What About Canada?

Canada followed a similar timeline, often mirroring U.S. regulations to maintain fuel and emissions compatibility across borders. 

Key dates:

2006: Canada required ULSD for on-road vehicles.

2007–2010: Canadian diesel generators and off-road engines started phasing into ULSD use.

By 2010, most on- and off-road applications had to use ULSD.

Since 2014, ULSD is mandatory across the board in Canada for all on-road and off-road uses, including generators, heavy equipment, and industrial machinery.

Environment and Climate Change Canada (ECCC) enforces these regulations, which align closely with EPA standards in the U.S.

What If I Use High-Sulfur Diesel in a Generator?

Running non-ULSD in a generator designed for ULSD can also damage the engine, clog emissions systems, and void warranties.

In short: use only ULSD, unless you’re operating an antique off-grid diesel engine in the middle of nowhere-and even then, it’s a risk.

ULSD and Emission Systems: What’s the Connection?

ULSD isn’t just cleaner-it’s essential for modern emissions control systems like:

• Diesel Particulate Filters (DPF)
• Selective Catalytic Reduction (SCR)
• Exhaust Gas Recirculation (EGR)

These systems are sensitive to sulfur. Using higher-sulfur fuel will clog and destroy them over time, leading to breakdowns and expensive repairs.

So, if you’ve got a diesel generator made after 2010, it requires ULSD. There’s no way around it.

Final Thoughts

ULSD is not a suggestion-it’s the standard across Canada and the U.S. Whether you're fueling a transport truck, a stationary generator, or a piece of construction equipment, you’re expected to use ultra-low sulfur diesel.

Aside from compliance, it’s just good practice. Cleaner fuel means fewer emissions, longer engine life, and less maintenance over time.

If you're buying or running diesel generators in North America, make sure your fuel supplier provides ULSD (they almost always do). And if you’re importing equipment, confirm that it’s compatible with North American fuel and emissions standards-especially if it was originally built for overseas markets with looser regulations.

Need help ensuring your generators are ULSD-compatible and compliant? Contact Masteraire today to get the right guidance and avoid costly fines.