Solutions For Reducing Marine Fleet Carbon Intensity


Expert Q&A explores viability of various lower carbon fuels

While international maritime fleets have been subject to increasingly stringent carbon intensity regulations in recent years, domestic inland fleets are in the early stages of being viewed with the same level of scrutiny. Even so, adoption of carbon reduction targets among private and public inland fleets is becoming increasingly common.

The regulatory landscape and market pressures have prompted both inland and ocean marine fleet owners to evaluate a variety of lower carbon solutions. Bio-based fuels have consistently risen to the top in terms of immediate viability and effectiveness.

For an in-depth look at all the solutions and why bio-based fuels are viewed to be an effective option, we conducted a Q&A with Jon Scharingson (JS), Executive Director, Strategic Initiatives at Chevron Renewable Energy Group.

Chevron employee Jon Scharingson headshot 

Jon Scharingson, Executive Director, Strategic Initiatives
Chevron Renewable Energy Group

Q: What is driving the need for marine fleets to lower their carbon intensity?

JS: For international maritime fleets, IMO 2020 and its recent update, IMO 2023, have been among the biggest drivers. These are regulations put in place by the International Maritime Organization (IMO) to help achieve a 40% reduction in carbon intensity by 2030 and a 70% reduction by 2050 as compared to 2008 levels. IMO 2023 includes a new index by which individual ships must be evaluated called the Carbon Intensity Indicator (CII). With the CII, every individual vessel will be given a grade from A to E — E being the worst — which is based on its GHG emissions in relation to the amount of cargo carried and distance traveled.1 Any vessel that receives a grade of D or below for three consecutive years will be required to take corrective action, which could include updating the vessel, replacing the vessel or integrating more lower carbon fuel solutions, such as biodiesel.

In addition to regulations, more than one-third of the major maritime shipping companies have set goals to reach net zero or have aligned with IMO goals.2 These IMO regulations and the movement to adopt carbon reduction targets have had a big impact on the demand for biofuels. In fact, Chevron Renewable Energy Group has already supplied millions of gallons of biodiesel into the marine market since IMO 2020 was put in place.

For domestic and inland fleets, IMO 2023 doesn’t apply, but with the Biden administration’s stated commitment of reducing U.S. GHG emissions by 50% by 2030 and reaching net zero by 20503 – pressure is mounting in the transportation sector, including the domestic marine sector.

Q: What are some of the alternative fuel solutions being explored for marine? How do they compare?

JS: A range of energy sources are being evaluated as lower carbon alternatives to marine diesel. Those include biodiesel, liquefied natural gas (LNG), methanol, ammonia and hydrogen. While some of these fuels are already being used in ocean maritime fleets, their use in inland, domestic fleets comes with a set of other challenges, including tank storage requirements in relation to vessel size, as well as the long life-span of marine vessels and the cost to retrofit. A recent report developed by Vanderbilt University for the American Bureau of Shipping (ABS) titled, Decarbonization of the Inland Waterway Sector in the United States, included a deep-dive evaluation of each of these lower carbon solutions.

Here are some key takeaways from that report, as well as other sources exploring the potential of each fuel for both inland and ocean fleets:

Connect With Marine Experts

Energy density and fuel tank capacity are key considerations

The lower the energy density of a fuel, the more fuel tank capacity required to achieve the same power of marine diesel. Only biofuel (biodiesel) can deliver nearly equivalent power to marine diesel using the same volume and fuel tanks. Not only would other fuels require more tanks, since upwards of 75% of fuel carried in the fuel tanks of inland boats is used as ballast fuel, the use of less dense fuels would require additional ballast tanks, which creates further concerns over the trim and freeboard.



 Fuel Energy Density as a Percentage of Marine Fuel
 Marine Diesel  100%
 Biodiesel 95% 
 LNG 54%
 Methanol 39%
Ammonia  39% 
Hydrogen  23%

Source: Decarbonization of the Inland Waterway Sector in the United States, P. 23



Biodiesel is a simple transition, providing lower carbon intensity today

Biodiesel can utilize a vessel’s existing fuel tanks, piping and engine, generally without any modifications or additional investments. With a density nearly identical to marine diesel, biodiesel wouldn’t require any additional tank storage. Biodiesel is also effective at reducing carbon intensity. In fact, compared to petroleum diesel, biodiesel may reduce carbon emissions by up to 100% for fossil carbon4 and 70% for total hydrocarbon.5 Additionally, studies have found that compared to electric-powered vehicles, biodiesel may be about 56% more effective at reducing carbon when taking the power grid into consideration.6

LNG is increasingly used in ocean fleets, but is less feasible for inland

When compared to hydrogen, methanol and ammonia, LNG has been adopted at the largest scale thus far for ocean fleets, thanks to its availability, lower cost than marine diesel and ability to reduce carbon emissions7. For inland, however, the Vanderbilt study cites a number of reasons when concluding that LNG would be, “unlikely to be adopted in the inland waterway sector” — namely due to tank storage and infrastructure challenges.

Methanol presents potential with modifications to infrastructure and vessels

Major maritime shipper, Maersk, is among the first to announce their plans to both retrofit existing vessels8 and order new vessels powered by methanol.9 Unlike LNG, methanol can be stored at ambient temperature, however, with a lower energy density, it would require 2.5 times the tank volume, thus, the Vanderbilt report concluded methanol could only be a solution for inland, “if fuel tank volume on board is increased, if vessels are used in less intense fuel consumption routes, or if refueling frequency is increased.”

Ammonia and hydrogen are being explored, but are not ready for widespread adoption.

Both ammonia and hydrogen are zero-carbon fuels extracted from natural gas, and are in the very early stages of being explored as a lower carbon marine fuel. Chevron is at the forefront, having recently announced plans to conduct a joint study evaluating the potential development of a hydrogen and ammonia production facility on the U.S. Gulf Coast.

Q: Given the options, which solution do you believe is most viable for widespread adoption today?

JS: While we support the advancement of all carbon reduction solutions, many of the ones being discussed are either in the early stages of development or may require retrofitting and/or investment in entirely new vessels. Given the incredibly long lifespan of these vessels, we expect that diesel-powered marine engines will be around for a long time. As long as that’s the case, a transition to biodiesel is the simplest way to lower carbon intensity today without any additional investment in engine technology, storage tanks or infrastructure.

Q: At what blend levels do you recommend introducing biodiesel into marine fleets?

JS: Both biodiesel and renewable diesel blend well with existing marine fuels like marine gasoil (MGO) and low sulfur fuel oil (LSFO). It’s common for our marine customers to blend at up to B30 (30% biodiesel to 70% MGO or LSFO). Blends of biodiesel up to B30 have also been approved by the International Convention for Prevention of Pollution from Ships (MARPOL). However, we have many customers that have successfully trialed the use of B100 (100% biodiesel) in their marine fleets. Most marine engines can also readily utilize biodiesel and renewable diesel blends, like our proprietary fuel we call UltraClean BlenDTM.

Q: What advice would you have for someone in the marine transport industry who may be hesitant about transitioning to biodiesel?

JS: Reach out to us. We would love the opportunity to address any questions or concerns. Ultimately, we’re confident that biodiesel is one of the simplest solutions for reducing carbon intensity in the marine industry today.

Ready to get started?

Contact us to discuss how we can be your lower carbon partner.

Footnotes and sources


DHL IMO 2023 Briefing



Product is produced from renewable oils and fats. Methanol used to make biodiesel and hydrogen used to make renewable diesel and SAF are typically made from conventional natural gas but can be produced from renewable resources.

5 CARB Assessment of the Emissions from the Use of Biodiesel as a Motor Vehicle Fuel in California "Biodiesel Characterization and NOx Mitigation Study." Durbin (2011)

Carbon intensity for EVs based on eGRID 2020 figures and EV EER of 3.8 for transit buses per National Renewable Energy Laboratory