Global warming, dirty air and the skyrocketing cost of petroleum are a volatile combination that easily leads to wishful thinking when it comes to the promise of a painless solution, and just as easily leads to a backlash of blanket condemnation. But biodiesel is neither the cure for all the economic and environmental woes caused by petroleum, nor is it a fraud foisted on ignorant consumers eager for the latest green fad.

Tamp down the emotion and ignore the speculation, though, and a realistic appraisal of biodiesel emerges, a view that shows a transportation fuel with great potential and great challenges. Biodiesel certainly could become one of the key alternative fuel sources that reduce our reliance on petroleum. And it just as certainly faces technological and logistical hurdles that could relegate it to a long list of impractical energy experiments.

To understand the whole story about biodiesel, you need to start with an objective look at its current successes and limitations, followed by a balanced evaluation of developing technologies that could overcome many of those limitations. That's not as easy as it sounds because a wide range of interested parties — from farmers to petroleum refiners to entrepreneurs — have geared up impressive publicity machines touting their particular viewpoints, often conveniently overlooking the negatives of their favored solution and all too often unrealistically touting advantages that have yet to be proven.

A Federal mandate that sets ambitious requirements for renewable fuel use by 2012 has also raised the stakes for those eager to claim the financial rewards that come with a practical solution for the U.S.'s sizeable petroleum appetite.

A more balanced evaluation of biodiesel starts by answering two basic questions: what is biodiesel and why has it generated so much enthusiasm?

In technical terms, biodiesel is a fatty acid methyl ester (FAME) produced from vegetable oils or animal fats through a transesterification process and meeting the D6751 specifications set by the American Society for Testing and Materials (ASTM). In simpler terms, it's plant oil or animal fat transformed with a relatively simple chemical reaction to create a non-petroleum fuel for diesel engines.

Just to confuse matters, there are other ways to create diesel-like fuel from the same “biomass” sources, but these are not technically biodiesel because they do not use transesterification and are not fatty acid methyl esters. These are called “renewable diesel” and may play an important role in the near future, but we'll save that discussion for later.

The most common sources for the vegetable oil used in biodiesel are soybeans in North America, rapeseed in Europe and palm in Asia. Animal fat is not widely used in commercial biodiesel production for a variety of performance and processing reasons, although at least one commercial operation in Hawaii is producing biodiesel from animal sources. Much research is underway to find other sources for biodiesel “feedstocks,” as both the volume and cost of the renewable basic materials are pivotal issues in the potential success of non-petroleum fuels.

While pure or 100% biodiesel (called B100) can be used to run a diesel, that's not recommended by engine manufacturers, and so it is generally blended with petroleum-based diesel. Currently, the most common biodiesel blend offered for on-highway vehicles is B5, which means it is 5% biodiesel, 95% petroleum-based diesel. However, blends as high as B20 are being used by a number of fleets. And in a long-awaited move by ASTM, in late June the standards group agreed on specifications for B6 to B20, which is widely expected to encourage wider acceptance of higher biodiesel blends as a transportation fuel.


Some of the benefits of biodiesel are immediately measurable, while others are long-range or more speculative. The most immediate can be measured at the tailpipe. Compared to petroleum diesel, a B20 blend reduces unburned hydrocarbons (HC) by 20%, particulate matter (PM) by 12%, and carbon monoxide (CO) by 12%. All three are regulated by the Environmental Protection Agency, with HC contributing to ozone-creating smog, CO a poisonous gas, and PM found to be a health hazard.

It seems likely that the fourth EPA-regulated diesel emissions — oxides of nitrogen or NOx — may actually be increased by biodiesel. Although studies aren't conclusive yet, some show soybean-based biodiesel and older engines to exhibit the largest NOx increase, while other biodiesels and engines show virtually none. Biodiesel also reduces some non-regulated tailpipe emissions that have been identified as harmful to health.

Blending biodiesel into diesel also improves fuel lubricity, which can be significant since the move to ultralow sulfur diesel (ULSD) had the opposite effect. More importantly, with blends of B20 or lower, biodiesel can be used in existing engines without any modification, a major benefit for fleets that have to comply with Federal alternative fuel requirements. Other alternative fuels require substantial changes to engines and fuel systems, but no new trucks or engine technology need to be developed to make the switch to biodiesel.

And perhaps the most attractive feature of biodiesel as an alternative fuel is that it can simply be “dropped in” to much of our existing fueling infrastructure, including tankers, fuel pumps and most storage tanks. The only exception is transportation via multi-product pipelines because of concerns about jet fuel quality, though there are discussions underway to address those concerns and open pipelines to biodiesel.

The clearest long-term benefit of biodiesel would come from a reduction in carbon dioxide (CO2), a major greenhouse gas. While burning biodiesel and petroleum-based diesel both release CO2 into the atmosphere, the plants used to create biodiesel remove CO2 from the air, creating a “closed carbon loop.” Compared to a fossil fuel like regular diesel, which only adds CO2 to our environment, biodiesel's closed loop reduces net CO2 emissions by an estimated 78%, according to the National Biodiesel Board (NBB).


The other major long-term benefit is more potential than certainty at this point. The U.S. currently consumes over 20 million barrels of liquid fuel a day, according to the federal Energy Information Administration (EIA), and over half of it is imported. Transportation accounts for 68% of that consumption, mainly through gasoline, ULSD and jet fuel. When fuel was still at $90 a barrel, our national bill for imported oil was around $250 billion a year. At $135 a barrel, add 50% to that figure.

The 2008 annual energy outlook from EIA projects that U.S. liquid fuel use will grow to 26 million barrels a day by 2025, 60% of it imported and transportation claiming 73% of the total.

As the current runup in crude oil prices so clearly indicates, America's need for imported oil creates both political and economic security concerns. Proponents of biodiesel say a fuel made from materials grown locally can address those concerns. And as a renewable fuel, they point out, biodiesel has the additional advantage of filling in for projected shortfalls as we consume our non-renewable fossil fuels.

Projections by EIA, however, reveal the weakness in that argument. In 2006, biofuels made up only 4% of the gasoline and diesel used in transportation, or 136 billion gal., according to the administration's outlook. Nearly all of it was ethanol blended with gasoline, with biodiesel accounting for only 300 million gal. By 2030, the U.S. will get 17%, or 25.8 billion gal., of its transportation fuel from biofuels, but biodiesel will only contribute 3.8 billion gal. to that number, EIA projections show. That's a little more than a drop in the bucket, but hardly a guarantee of energy security.


Assessing biodiesel's shortcomings starts with the warning that this is a rapidly developing new technology. Some concerns about the suitability of biodiesel for everyday truck fleet operations are based on outdated information drawn from experiences with early technologies. Some are based on half-truths or lack of experience with biodiesel. Some are based on the characteristics of pure B100 and disappear with the more commonly used blends of B20 or lower. But some problems are real and substantial, and it's still too early to tell if these challenges can be overcome with further development.

One common objection to biodiesel is poor cold-weather performance. This can be classified as one of the half-truths. Biodiesel does gel in cold weather, but standard No. 2 diesel also gels when temperatures drop, and blending with No. 1 diesel or cold-flow additives is required in many colder areas during winter months. However, B20 begins exhibiting cold-weather problems 2 to 10 deg. F before petroleum diesel, and its cold-flow properties vary substantially depending on the feedstock used. And the poor cold-weather properties of pure B100 is one major reason B20 is seen as the most practical way to use biodiesel in vehicles.

But this is far from a deal-breaker. Some fleets currently using B20 as their standard fuel simply switch to B5, which they say has the same cold-weather performance as standard diesel. And NBB says the same cold-weather solutions used for standard diesel work well with B20, too.

Another widely held half-truth is that biodiesel can create filter plugging problems. Biodiesel is a better solvent than diesel, which means it can dissolve sediment in storage tanks and fuel lines, carrying them to filters. However, if there is a problem it's usually seen only when a fleet initially switches to biodiesel and it's usually not an issue with blends of B20 and lower.

B100 can deteriorate engine gaskets, hoses, seals and other elastomers or rubber compounds used in engines, but again B20 blends and below seem to minimize or eliminate that problem. According to the Dept. of Energy, the problem is primarily seen in older engines built before 1993. The industry's switch to ULSD has also led manufacturers to switch to materials that should be more compatible with biodiesel as well.

Concerns over warranty coverage are also abating. Initially, most engine makers would only publicly commit to honoring warranty claims when biodiesel was used in B5 blends or lower, though some extended that up to B20 in certain cases. The new ASTM specs for B6 to B20 approved in June should quickly lead all to add the higher B20 limits to standard warranty coverages.

Storage can also present some minor problems. NBB recommends that biodiesel stored longer than six months be treated with antioxidants and tested to be sure it still meets ASTM specs. Some storage tank materials such as concrete are also considered unsuitable for biodiesel, although steel, aluminum and other common tank materials are fine.

A more substantial criticism of biodiesel is that it contains less energy than diesel from petroleum. DOE documents estimate that No. 2 diesel has 8.5% more energy per gallon than B100. As Gary M. Parsons, a research engineer with the lubricant additive company Chevron Oronite LLC, explains, the higher oxygen content of biodiesel, which gives it superior emissions performance, also results in lower energy density. By his calculation, one gallon of No. 2 diesel contains 129,050 Btu, compared to 118,170 for a gallon of B100.

In blends up to B20, Parsons, NBB and others say the difference in perceived power and fuel economy is not noticeable. Given the large amounts of fuel consumed by truck fleets, however, even a small decrease in fuel economy can have large cost impacts.


These are all relatively minor issues that proponents of biodiesel say are overshadowed by its benefits; however, there are three major impediments to widescale adoption of biodiesel in the near future that are not so easily dismissed — cost, quality and supply.

Biodiesel costs more to manufacture than petroleum diesel, about $1 to $2/gal., according to DOE estimates last year. With crude oil hitting $140 a barrel in June and July, it would seem that the cost difference would shrink, if not disappear, for a non-petroleum competitor. However, soybean and other vegetable feedstock sources are also commodities and are generally experiencing similar runups in cost. Since feedstock prices account for up to 80% of biodiesel's cost, there's little opportunity to shrink the price spread.

The impact of that high cost means that even in its early stages, the biodiesel industry has far more production capacity than buyers for its product. In January, NBB said there were 171 companies in the U.S. with a total production capacity of 2.24 billion gal. a year. But actual production was only 500 million gal. in 2007 and is only expected to grow to 550 million gal. this year, according to the trade group. And that's with federal tax incentives of up to $1/gal. in place, incentives intended to be temporary.

The relative simplicity of manufacturing biodiesel, at least from high-quality vegetable oils such as soybean and rapeseed, and unrealistic expectations for rapid market growth not only brought about exuberant investment in biodiesel capacity but have also created quality problems. In fact, critics say widely varying quality should be users' largest concern when considering biodiesel.

ASTM standards for B100 were a good first step in addressing the quality issue, and the new B6 to B20 specs should improve user confidence since most purchase biodiesel as a blended fuel. But to ConocoPhillips' biofuel manager Lou Burke, just meeting specs isn't enough. The manufacturing process control also has an impact on final performance, as does storage, testing, blending, shipping and other fuel management practices.

Parsons cites an NBB-funded quality testing project that found 59% of biodiesel samples taken in late 2005 and early 2006 were out of spec due to processing issues alone. NBB has created an accredited quality assurance program, BQ-9000, for both manufacturers and marketers to address the issue. A similar program has been created in Germany and Austria that even extends to service stations retailing biodiesel products.

Petroleum diesel can certainly suffer from quality problems, but, in general, users expect and get uniform quality in their diesel. With biodiesel, at least at present, they need to ensure it meets the accepted specifications and quality standards.


The third problem facing biodiesel is the most contentious and the most serious. Like the other major biofuel ethanol, biodiesel currently relies on food crops for most of its raw material. The “food vs. fuel” debate is too complex to go into detail, and it is being played out on a global scale that is far beyond the scope of this article. In general terms, there is growing concern that we should not divert valuable food resources to solve energy problems.

What fleet and other users of biodiesel should recognize, though, is that the vegetable oils most commonly used for biodiesel are not only expensive, but there is a finite supply limited by the agricultural resources needed to grow them. In other words, we don't have enough resources to replace a significant portion of our petroleum-based diesel with biodiesel made from valuable food crops.

NBB and others point to work currently underway to use non-food plant oils, and waste or animal fats to make biodiesel. Researchers such as Michael Briggs, a chemist from the University of New Hampshire and co-author of a number of published studies on biodiesel production, point out that those materials have even higher processing costs and require additional steps to remove unwanted by-products.

Further research might overcome those problems, but a more basic one remains. It's not clear that any crop or even waste material currently under consideration could ever support widescale use of biodiesel. Just consider soybean oil, one of the easiest to convert and lowest cost feedstocks for biodiesel. According to Briggs' calculations, one acre of soybeans yields only 60 gals. of biodiesel per year.

Or as Lou Burke puts it, there just isn't enough base material for biodiesel to make much of a dent in our petroleum use.


We shouldn't count out biodiesel just yet, though. There are some early, but promising, developments that might solve the cost, quality and supply issues, making biodiesel or a new generation of renewable diesel fuels a key element in future energy supplies for transportation.

One unlikely inspiration for this optimism is algae. It grows quickly in places and under conditions unsuitable for food crops, and certain strains contain high amounts of oil for transformation into biodiesel. A number of projects cultivating algae crops in everything from polluted ponds to enormous tubes are underway around the world.

Like the earliest days of biodiesel, there are already performance claims for algae that defy even the most optimistic calculations. Still, theoretical yields are being calculated in the tens of thousands of gallons per acre per year, far above soy's 60.

Even if the early work bears fruit, commercial volumes of algae-derived diesel are still years away. But, says Burke, “if algae becomes big, it certainly could supply a substantial portion of our energy.”


The other promising avenue is the development of what is being called “second-generation biodiesel” or “renewable diesel.” It can start with the same biomass materials as the current biodiesel product, including algae, but both the chemical process and end product are quite different.

Avoiding the chemistry lesson, renewable diesel is created using a process developed to make synthetic diesel out of coal, but using plant and animal oils and fats. Instead of the transesterification process used to create biodiesel, renewable diesel is refined much like crude oil and produces a fuel that is chemically identical to petroleum-based diesel.

“We make diesel fuel molecules,” says Burke, whose company is currently producing renewable diesel at a ConocoPhillips refinery in Texas from pork and animal fat supplied by Tyson Foods. The yield is low — 300 barrels a day — and the cost of both the fat and the refining process is considerably higher than with petroleum. Similar pilot projects are ongoing in Europe.

Being the chemical twin of the petroleum fuel gives renewable diesel some potential advantages over first-generation biodiesel. As a refined product, quality and performance properties are independent of the feedstock, which means fewer unexpected surprises for users. As a synthetic product, it is a high quality fuel with 90 to 100 cetane ratings, no oxygen or sulfur, and no paraffin to create low-temperature gelling, according to Burke. It can also be transported in pipelines just like diesel and is completely compatible with any diesel engine.

At present, the refining process is considerably more expensive than biodiesel's transesterification, and it doesn't offer the same tailpipe emissions benefits. More importantly, renewable diesel faces the same feedstock limits as biodiesel.

If algae doesn't live up to its promise — and there are some well-respected critics who don't believe it will — a third-generation biodiesel currently being studied could solve the feedstock problem. Called biomass-to-liquid (BTL), it can use straw, timber, wood chips, plant waste, manure and a wide range of cellulose sources to create renewable diesel. As the name suggests, the process turns cellulose into a gas which is then converted to synthetic diesel.

Easy to describe, but far more complicated to do. And with complexity comes expense. Still, BTL offers potential because it can be derived from material we now throw away, which could lower costs and ease competition between energy and food. A number of demonstration projects are currently up and running, most funded by tax incentives. It remains to be seen if BTL can make the transition to significant commercial production.


It's clear that the U.S. and other industrial nations need to find alternatives to petroleum. As a major consumer of oil, most of it in the form of diesel, the trucking industry is right at the front of that search.

Biodiesel offers fleets an extremely attractive road map to renewable energy because it requires the fewest changes to current vehicle technology and distribution systems, while also promising important environmental advantages. It deserves serious consideration as a key element in our efforts to develop new energy sources for our transportation needs.

Despite the urgency created by rapidly rising oil costs and growing concern over global warming, trucking also needs to take a step back from the alluring promise of biodiesel for a moment. Biodiesel could well be the fuel of the future for your trucks, but it's far from a finished product no matter what its proponents may claim. If you're going to make the right decision, you need a realistic understanding of its weaknesses as well as its strengths. You need, and deserve, the whole story.


Given the wide variety of sources offering competing, and often biased, information on biodiesel, I have avoided citing specific sources. Instead, I have attempted to create a more objective evaluation by a consensus view based largely on the following sources:

  • Interview, Michael Briggs, PhD, Dept. of Physics, University of New Hampshire

  • “Biodiesel production — current state of the art and challenges,” Journal of Industrial Microbiology, Briggs and Palligarnai T. Vasudevan, University of New Hampshire

  • Interview, Lou Burke, manager of biofuels, ConocoPhillips

  • Biodiesel and Engine Lubrication, Gary M. Parsons, global industry liaison manager, Chevron Oronite LLC

  • Interview, Jennifer Weaver, spokesperson, National Biodiesel Board

  •, National Biodiesel Board

  • Annual Energy Outlook 2008, U.S. Dept. of Energy/Energy Information Administration

  • Renewable Fuel Standard Implementation: FAQ, U.S. Environmental Protection Agency/Office of Transportation and Air Quality