“It absolutely helps that the national and California-based fleets’ resources are no longer solely devoted to Advanced Clean Fleet [regulations],” he said.

Many see the fuels as more than a bridge to other technologies, said Josh Tippin, vice president of fuels and energy at Penske Transportation Solutions.

“There is no silver bullet to tackle this, and because we’re so entrenched with the efficiency and the power of the diesel molecule, it’s really hard to replace,” he said, adding that decarbonization is going to take a multipronged approach.

Penske began distributing renewable diesel, also known as hydrotreated vegetable oil, or HVO, three years ago at fueling locations along the West Coast, and Tippin said interest has continued to increase.

“Companies that are trying to mitigate their [carbon dioxide] and [greenhouse gas] footprint ask us where they can get the product and how they can use it more often,” Tippin said, adding that Penske Truck Leasing’s fueling locations in California pump renewable diesel exclusively, which makes up about 10% to 15% of its total bulk fuel sales.

In addition to reducing GHG emissions, renewable diesel reduces particulate matter by more than 40%, carbon monoxide by more than 25%, total hydrocarbons by more than 20% and nitrogen oxides by 10%, he said. It can be used in diesel engines in any concentration because it is chemically equivalent to petroleum-based distillate fuel.

“You don’t have to buy a new piece of equipment. You don’t have to change your infrastructure,” Tippin said. “It’s one of the only products that’s truly a drop in.”

Over the past three to five years, the supply of renewable diesel has increased dramatically.

“There’s been significant investments by the energy majors in developing resources and converting refineries to develop that market,” TRC’s Springer said. “Kudos to them that supply is reaching and beginning to saturate certain markets.”

The U.S. Energy Information Administration estimates that renewable diesel production averaged about 220,000 barrels a day in 2024, up from 170,000 in 2023. The agency’s May short-term energy outlook forecasts annual production will increase about 5% this year compared with 2024 due to increased capacity.

Despite the higher production levels, renewable diesel isn’t readily available outside of states with low-carbon fuel standards.

“The problem with it is that you can’t get it,” said Matt McLelland, vice president of sustainability and innovation at Covenant Logistics. “It’s generally available throughout California, Oregon and Washington state, but when you’re outside of those states, it is a challenge.”

Renewable diesel accounted for about 5% of Covenant’s overall fuel purchases last year.

The Chattanooga, Tenn.-based company ranks No. 35 on the Transport Topics Top 100 list of the largest for-hire carriers in North America.

Renewable diesel production tends to be coastal, where refiners can import large amounts of feedstock, or in markets with ample feedstock.

“Most production takes place in California and the Gulf Coast,” Penske’s Tippin said.

What’s more, changes to the $1-per-gallon biodiesel and renewable diesel blenders tax credit have affected the feedstock.

“It took away, in essence, availability outside of incentivized states,” Tippin said, adding that renewable diesel tends to be affordable only with subsidies.

NACFE’s Roeth said renewable diesel is the “easy button” if fleets can get it, but the cost of shipping it long distances can make it cost prohibitive.

“There are several fleets being asked to use it by their customers,” he explained. “By the time they tell them that getting renewable diesel trucked in is going to cost an extra dollar or two a gallon and increase the cost of doing business, they’re not doing it.”

Making the Business Case

Economic pressures throughout the industry are also affecting adoption.

In April 2024, Volvo Trucks North America started fueling newly assembled trucks with HVO at its New River Valley assembly plant in Dublin, Va., but stopped doing so in July.

“We’ve temporarily paused the use of HVO for our factory fill as part of cost-cutting measures in response to the weak truck market,” said Allison Daigle, VTNA’s public relations manager. She said the fuel remains a good low-carbon alternative with many benefits, and Volvo supports “policies that would increase market supply and lower cost.”

Penske Truck Leasing is currently running a trial with one of its partners to quantify renewable diesel’s performance and benefits.

“In our own maintenance and testing, we don’t see any reason to disagree with the numbers that are published, but when you take a molecule like this, it almost has to be like-to-like every day to get that true test result,” Tippin said.

In this specific test, Penske’s partner is only buying renewable diesel from a dedicated tank and running the exact same model, make, mileage and nearly identical route as a truck using traditional diesel.

“We are, for lack of a better term, getting as scientific as we can get,” Tippin said.

The trial, now in its third month, is scheduled to last about a year, and the results are expected to be released in late 2026.

Apart from HVOs, some fleets are fueling their trucks with higher blends of renewable biodiesel made from sources such as vegetable oils, animal fats and recycled restaurant grease.

Covenant Logistics turned to high biodiesel blends to help a customer reduce indirect “Scope 3” emissions in its supply chain.

“The transportation buyer I was working with needed the best bang for his buck,” McLelland said. “I presented this to him, and, ultimately, they pulled the trigger on it.”

ADM Trucking, which has 50 units — about 10% of its fleet — running on a 99% biodiesel blend, said cost differences between high biodiesel blends and traditional diesel have been marginal. There have also been benefits in other areas.

“The operational differences are minimal, with more positives than negatives,” said Brandon Rick, fleet and sustainability manager for ADM Trucking.

ADM Trucking is a subsidiary of Chicago-based food and animal feed processing company Archer-Daniels-Midland Co., which ranks No. 80 on TT’s Top 100 list of private carriers.

Both Covenant and ADM are partnering with Optimus Technologies to expand the use of biodiesel in their operations.

While most diesel engine manufacturers support at least 20% biodiesel blends, Optimus Technologies’ Vector fuel system is designed to enable conventional diesel engines to run on up to 100% biodiesel, also known as B100, in a wide range of climates.

Concerns often remain when adopting new technologies, and one of the most common questions Optimus receives is about the impact of high-blend biodiesel on engine warranties.

“The short answer is no, it does not void the warranty,” Optimus CEO Colin Huwyler said.

Optimus has successfully integrated its bolt-on fuel system across a wide range of truck platforms, including Volvo, Mack, International, Freightliner, Peterbilt and Kenworth, and Huwyler said the company is always willing to work with manufacturers to ensure warranties remain in place.

International recently issued one of the clearest statements to date regarding Optimus, stating that “any vehicles that are upfit with the Optimus system to operate on 100% biodiesel will not have their warranties and/or extended service contracts from International Motors voided.”

Even so, some of the early challenges associated with biodiesel, especially with cold-weather starts and operations, have made some fleets hesitant.

“Many of the biggest concerns and challenges were addressed long ago,” TRC’s Springer said. “This is not new, and the data is there about their benefits, how to manage them and use them effectively.”

Systems from Optimus Technologies use integrated heat exchangers and software that prevent fuel gelling or filter clogging, even in temperatures as low as minus 35 degrees, ensuring dependable operation in extreme climates.

For fleets considering B100, ADM Trucking’s Rick recommends starting small by testing two or three units to understand the process before adding more vehicles.

“Focus on progress, not perfection,” he said. “Challenges will arise, but documenting and addressing them early helps ensure smoother scaling.”

As fleets gain more experience with biomass-based fuels, momentum continues to build.

“It was really Pepsi’s adoption of this product that allowed me to have the confidence that we needed in order for us to put it into a proof of concept and recommend it to a customer,” Covenant’s McLelland said, noting that Pepsi has more than 800 trucks running on high biodiesel blends. Pepsi did not respond to requests for comment.

ADM’s Rick said collective efforts also ease the transition.

“Collaboration is key,” he explained. “Coalitions of B100 users can pool fuel demand, making it attractive for retail providers to install B100 pumps at fuel islands.”

Penske’s Tippin said that until some of the economics on renewable diesel improve, incentives are needed to drive adoption.

“Unfortunately, biomass feedstock costs more than crude. It costs more to refine, and then you have the logistics of it,” he said. “The biggest thing that can help this product move along is for local people in their state to reach out to their congressional leaders and ask for this product or to be subsidized enough to bring it there.”