Explore the main types of marine fuels, their emissions impacts, and the strategies helping fleets cut pollution and prepare for decarbonization.
Not all marine fuels are created equal. And today, that matters more than ever.
With international regulations tightening, heightened concern over air quality in port communities, and growing pressure to reduce climate impacts, fuel has become a strategic decision. The type of fuel a fleet uses can determine compliance, operating costs, and public health outcomes.
Heavy fuel oil (HFO) still dominates global shipping for its low cost and wide availability, but it remains one of the most polluting options. Alternative fuels promise cleaner operations but face barriers around cost, availability, and infrastructure.
Every option carries trade-offs. Understanding the fuels that dominate shipping, the alternatives shaping its future, and the strategies available to help ships cut pollution is essential to preparing for long-term emissions reduction.
Marine fuels powering today’s fleets
Despite growing attention on emissions reduction, the global fleet still relies overwhelmingly on fossil fuels—making up roughly 85% of total marine fuel consumption. These legacy fuels are inexpensive and abundant but exact a steep toll on public health and the planet.
Exhaust from marine fuels is a leading source of sulfur oxides (SOₓ), nitrogen oxides (NOₓ), carbon dioxide (CO₂), and particulate matter (PM). These pollutants directly harm air quality in coastal communities and port cities, driving health issues like asthma, lung cancer, heart disease, and premature death. On a planetary scale, these fuel emissions accelerate climate change, acidify oceans, and damage marine ecosystems.
This dependence on legacy fuels is one reason shipping accounts for nearly 3% of global greenhouse gas emissions—making it one of the largest single-sector emitters.
Today’s most common marine fuels include:
Heavy fuel oil
Heavy fuel oil (HFO), a residual byproduct of crude oil refining, is thick, inexpensive, and abundant, making it the go-to fuel for large ocean-going vessels. But it is also the dirtiest option, producing the highest levels of CO₂, SOₓ, NOₓ, and PM.
Marine gas oil
Marine gas oil (MGO) is a lighter distillate fuel refined directly from crude. It burns more cleanly than HFO and is commonly used in Emission Control Areas (ECAs) with strict sulfur limits. Still, MGO emits significant CO₂ and NOₓ, making it an unsustainable option for the future.
Liquefied natural gas
Liquefied natural gas (LNG) is natural gas cooled into liquid form for easier storage and transport. It reduces SOₓ, NOₓ, and CO₂ compared to HFO and MGO, but its climate advantage is undermined by methane slip—the release of unburned methane. Despite this, LNG remains popular for vessels designed with dual-fuel capabilities.
Marine fuels of the future: long-term transition options
No single alternative has emerged as the winner, but several options are being tested as long-term pathways toward a zero-emissions future:
Methanol
Methanol can be produced from biomass, captured carbon, or natural gas, and is already scaling commercially, with a growing number of dual-fuel vessels in service. Methanol can reduce CO₂, SOₓ, and NOₓ emissions, and when made with renewable energy and captured carbon it offers substantial climate benefits. The challenge lies in production pathways: fossil- based methanol, derived from natural gas, extends reliance on fossil resources and delivers only limited emissions reductions.
Hydrogen
When produced from renewable electricity, hydrogen can be used in engines without producing CO₂, SOₓ, or NOₓ. But scaling it up is difficult—hydrogen requires large amounts of clean power, and storing it onboard is complex because it must be kept at extremely cold temperatures.
Ammonia
Ammonia, which can be made from hydrogen, eliminates CO₂ emissions entirely and offers higher energy density than hydrogen, making it appealing for long trips. But ammonia is highly toxic, raising serious safety and handling concerns.
Biofuels and synthetic fuels
Produced from renewable sources like plant oils, agricultural waste, or captured carbon, many of these fuels can be used in existing ship engines with little to no modification. Still, not all pathways are sustainable. Certain biofuels, such as those made from palm oil, contribute to deforestation and compete with food crops. Synthetic fuels avoid these trade-offs but remain costly to produce and are only available in limited volumes today.
Bridging the gap: reducing fuel-related emissions today
Because cleaner fuels are years away from wide-scale adoption, operators are using transitional strategies to reduce emissions now:
Fuel-switching and dual-duel ships
Many vessels switch between conventional fuels and cleaner alternatives when operating in regions with stricter emissions standards. Dual-fuel ships extend this flexibility: they can run on traditional fuels today while being designed to transition to future alternatives. While both strategies provide compliance pathways, they remain costly and constrained by fuel availability.
Exhaust treatment systems
Exhaust gas cleaning systems, like scrubbers, work by spraying seawater or an alkaline solution into the exhaust stream, which traps SOₓ and PM before they are released into the air. They offer a relatively low-cost option that helps ships comply with current sulfur regulations without switching to more expensive fuels. Still, scrubbers often complicate operations, require frequent maintenance, and generate waste byproducts..
Shore power
Shore power lets vessels shut off their engines and plug into the electrical grid while docked, cutting local air pollution and protecting community health. However, this strategy only works when ships are at berth, not at sea. It draws energy from the grid, which often uses non-renewable energy. Shore power typically requires major investments in port infrastructure and vessel retrofits, making adoption unevenly disrupted and expensive.
Emissions capture and control
Emissions capture and control directly removes pollutants before they exit the exhaust stack. Unlike shore power, which only reduces emissions while a vessel is docked, this technology works both at sea and in port. These systems provide fleets with a practical way to meet today’s regulations without waiting for new fuels or infrastructure. Critically, emissions capture works across all major vessel types, making it one of the most versatile solutions available today.
Complementing emissions capture and control, carbon capture systems aim to trap CO₂ emissions onboard before they escape into the atmosphere. The technology is still in its early stages, with projects underway to test capture efficiency, onboard storage, and safe offloading of CO₂.
How STAX bridges the gap to sustainability and compliance
The clean fuels of the future will take decades to scale. But ports and fleets don’t have decades, they need solutions now.
STAX provides that bridge. By capturing harmful pollutants directly at the source—including the expansion of on-board carbon capture technology—STAX enables fleets to reduce emissions without waiting for alternative fuels or new infrastructure. This means immediate reductions in emissions that drive climate change and harmful air pollutants that affect community health.
Proven in California, the world’s strictest emissions regulatory environment, STAX technology has already demonstrated safety, reliability, and compliance. As global regulators tighten emissions rules, STAX is expanding into new regions to support ports and carriers worldwide.
For operators balancing compliance, cost, and sustainability, we deliver a solution that works today and adapts to tomorrow—helping fleets protect community health and make measurable progress toward decarbonization.
Discover how STAX’s technology can help your fleet achieve sustainability goals and meet compliance requirements.
