In this episode of Sustainability in the Air, Bruce Fleming, CEO of Montana Renewables, speaks with SimpliFlying’s CEO Shashank Nigam about how one of the largest sustainable aviation fuel (SAF) producers scaled its operations by leveraging existing infrastructure rather than starting from scratch.
Montana Renewables (MRL) is an unrestricted subsidiary of Calumet, which developed the business by converting a portion of its crude oil refinery in Great Falls, Montana. The facility now processes a range of feedstocks, including used cooking oil, agricultural waste and emerging crops, into SAF, renewable diesel and renewable hydrogen.
Here are the key highlights of the conversation:
Montana Renewables’ origin and the retrofit model (2:48)
Scaling from 30M to 300M gallons: what it actually involves (7:54)
The policy landscape and why private capital has withdrawn (10:05)
Feedstock agnosticism and the camelina case (22:16)
Why the EU’s RFNBO mandate is “preposterous” (28:54)
The case for fuelling general aviation first (38:30)
The SAF industry in 2035 and beyond (45:16)
Rapid Fire! (48:31)
Keep reading for a detailed overview of the episode.
Why parallel refinery systems matter for scaling SAF production
Much of the current momentum around SAF production has focused on new, purpose-built plants. Montana Renewables took a different route. Instead of starting from scratch, it reconfigured part of an existing refinery, and adapted established infrastructure to process renewable feedstocks.
The capital case for this approach is obvious. A retrofit costs significantly less than a greenfield build: the site, civil works, safety systems and workforce are already in place. Moreover, if a large refinery converts entirely to renewable operations, the overall transportation fuel output can fall sharply, says Fleming.
MRL avoided that trade-off by operating two distinct businesses on the same site: a conventional refinery alongside a separate renewables line, supported by a shared workforce and common operating standards.
Fleming positions MRL’s approach as a model that could be applied wherever suitable refinery infrastructure already exists:
“We’ve demonstrated how renewables can be integrated into refinery operations without sacrificing transportation fuel output. This could significantly influence long-term fuel costs across the entire ecosystem, and we see strong potential for others to replicate this approach.”
4 ways Montana Renewables is redefining SAF production
1. The retrofit model at commercial scale
Montana Renewables operates two distinct but co-located operations at its Great Falls site: a conventional crude oil refinery and a renewables facility.
The facility is currently permitted to process about 250 million gallons of renewable feedstock annually, with plans to expand that to roughly 300 million gallons. This increase requires only a modest uptick in overall throughput, with the more meaningful change coming from optimising the product mix, explains Fleming.
With nearly four years of operating experience, the company has also identified specific constraints and bottlenecks in its process. While MRL’s current economic SAF yield is around 50 million gallons per year, it expects to increase this output by reconfiguring the process to favour SAF, rather than materially increasing total input.
“Depending on market conditions and demand, we have the flexibility to tailor the output so that up to 90% of the feedstocks come back as SAF,” says Fleming.
MRL is one of a small number of projects to secure a US Department of Energy loan guarantee, following several years of due diligence. Financially, it is already showing signs of resilience. Fleming notes that through the first three quarters of 2025, Montana Renewables was cashflow positive, a position he believes very few comparable SAF operations have achieved.
2. Feedstock agnosticism
MRL can process a wide range of inputs: used cooking oil, conventional vegetable crops, agricultural waste and emerging cover crops. Fleming describes these feedstocks as largely interchangeable from an operator’s perspective. Each requires pre-treatment and careful handling through a sensitive catalytic process, but the choice between them is driven by economics rather than technical constraints. If a buyer specifies a particular feedstock, the company can accommodate it; the added constraint is simply reflected in the price.
“We don’t care what feedstock we put into the machine. All of these are essentially interchangeable to an operator like us.”
He points to camelina — a cover crop that can be grown without displacing primary food production and has a relatively low carbon intensity — as an example of how the feedstock base could evolve. MRL, Fleming says, was one of the first companies to have produced SAF from the crop.
Fleming uses this to challenge a common concern in SAF debates: that scaling production will compete with food for land. His view is that agricultural productivity in North America has increased faster than food demand for decades, leaving more land available. In that context, he sees the food-versus-fuel framing as an oversimplification of a more dynamic system.
3. Why policy volatility is limiting capital for SAF
Fleming expresses concern around feedstock regulations. Supply chains, he argues, take years to adjust. Once a jurisdiction restricts which feedstocks can be used for specific applications, commercial operators, including growers, transporters, and producers, adjust their supply chains to work around those limits.
“You cannot over-constrain an industry that is still in an experimental phase by micromanaging which feedstocks are allowed for targeted applications.”
The result is that global supply still meets demand, but through longer and more costly routes. Feedstocks are re-routed across regions and end uses to comply with local rules, often through longer and less efficient pathways. That added complexity feeds directly into higher costs and weaker economics. This also affects investments significantly.
For all the political support behind the energy transition, the investment climate for SAF is, in Fleming’s assessment, close to paralysed. “There is effectively zero private capital available at this time.” Fleming attributes this not to a lack of confidence in the energy transition, but to the difficulty of modelling returns in a constantly shifting policy environment.
Fuel infrastructure requires capital commitments over decades, yet the regulatory frameworks governing SAF continue to evolve on much shorter timelines. Incentives such as US producer tax credits and Renewable Identification Number (RIN) markets, alongside parallel schemes in other regions, are all evolving, often without coordination.
“Without policy stability over a decade or more, investment will not extend beyond early-stage seed capital,” he explains. In practice, that leaves early-stage venture capital as the dominant source of funding, while large-scale projects struggle to secure financing.
4. Book-and-claim can materially reduce SAF costs
Fleming is a strong advocate for book-and-claim, framing it as a logistical solution rather than a purely accounting mechanism.
Today, SAF transactions are often constrained by requirements around traceability and physical linkage, which can result in fuel being transported over long distances to match specific buyers.
Moving fuel by truck or rail is significantly more expensive than pipeline transport, but pipelines do not preserve the identity of individual fuel batches. That creates a mismatch between physical distribution and emissions accounting.
Book-and-claim separates the two. The fuel is delivered wherever it is most efficient to do so, while the associated emissions reduction is allocated to the buyer through a certificate.
“The difference is about a dollar per gallon in the finished fuel, if I can avoid transporting materials across the country by truck and rail, which is inefficient, and instead use pipelines, which are more efficient.” At scale, that cost differential becomes significant; a structural efficiency gain rather than a marginal improvement.
Overall, Montana renewables’ approach points to a pragmatic route for SAF scale: build on existing infrastructure, retain flexibility, and align policy with investment timelines. Without that stability, the industry risks slowing just as it begins to prove what is possible.
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