Marine Cylinder Oil BN Grades: A Buyer’s Guide
Marine cylinder oil is the total-loss lubricant injected directly into the cylinder liners of large low-speed two-stroke crosshead engines, and the single most important specification a buyer must get right is Base Number (BN) — matched to the sulphur content of the fuel the vessel is actually burning, and cross-checked against the engine maker's current guidance for that engine mark. Get the BN wrong and a ship risks either inadequate acid neutralization (liner and piston-ring wear) or excess unneutralized alkalinity and deposit build-up on piston crowns. This guide explains how BN grades map to fuel sulphur under IMO 2020, what a No-Objection Letter (NOL) is and is not, how cylinder oil differs from system oil, and what a procurement team must specify — packaging, MOQ ranges, HS code, and export documents — before sending a Request for Quote through Altonex Global.
What Is Marine Cylinder Oil and Which Engines Need It?
Marine cylinder oil lubricates the cylinder liner, piston rings, and piston skirt of large low-speed two-stroke crosshead marine diesel engines — the main propulsion engines built to designs from MAN Energy Solutions (renamed Everllence on 4 June 2025) and WinGD (Winterthur Gas & Diesel). It is an all-loss (total-loss) lubricant: injected through lubricator quills directly onto the liner wall and consumed and scraped away with every piston stroke. Unlike lubricating oils in most other machinery, it is never recirculated or filtered back into service.
This total-loss design is deliberate. It lets the cylinder circuit absorb the acidic combustion by-products of burning sulphur-bearing marine fuel without mixing that contamination back into the engine's other lubricating circuits — which is also why cylinder oil formulation, and specifically its BN, has to track the fuel sulphur level closely.
Why Does IMO 2020 Determine Which Cylinder Oil BN a Ship Needs?
Since 1 January 2020, MARPOL Annex VI Regulation 14.1.3 — the IMO's "IMO 2020" sulphur rule — has capped marine fuel sulphur content at 0.50% m/m globally, down from the previous 3.50% cap, with a tighter 0.10% m/m limit inside Emission Control Areas (the Baltic, the North Sea, North American coastal waters, and the US Caribbean). The IMO states this global cap has cut sulphur-oxide emissions from shipping by roughly 70%.
That regulatory shift changed what most ships burn, and burning a different fuel sulphur level changes how much acid the cylinder oil has to neutralize. Base Number (BN, measured in mg KOH/g under ASTM D2896) is the industry measure of a cylinder oil's reserve alkalinity — its capacity to neutralize the sulfuric acid formed when fuel sulphur combusts in the cylinder. A vessel burning very-low-sulphur or ultra-low-sulphur fuel oil (VLSFO/ULSFO) needs a different BN than a scrubber-fitted vessel still burning high-sulphur fuel oil (HSFO). Getting BN selection wrong is a recognized risk factor in either direction — too low risks liner and piston-ring wear, while unnecessarily high BN on low-sulphur fuel risks unneutralized alkalinity and deposit formation.
How Do I Match Cylinder Oil BN to Fuel Sulphur Content? (BN 25 / 40 / 70 / 100 / 140)
Trade-press reporting on post-2020 lubrication practice describes the typical BN-to-fuel bands summarized in the table below. These are indicative bands, not a fixed universal rule — every purchase should be cross-checked against the current engine maker service letter for the vessel's specific engine mark before a BN grade is finalized.
| Cylinder Oil BN Grade | Fuel Type & Approx. Sulphur | IMO 2020 Context |
|---|---|---|
| BN 25 | ECA-grade ULSFO / marine distillate, ≤ 0.10% S | Emission Control Area limit |
| BN 40 (Category II) | VLSFO / ULSFO, 0.00–0.50% S | Global 0.50% cap — current mainstream grade for later-mark engines |
| BN 70 | Intermediate / transition fuels — verify with engine maker | Used in some blended or transitional-fuel cases |
| BN 100 | HSFO, scrubber-fitted vessels, approx. 1.5–3.5% S (indicative) | Scrubber (exhaust gas cleaning) compliance route, not a fuel switch |
| BN 140 | HSFO, scrubber-fitted vessels, approx. 1.5–3.5% S (indicative) | Scrubber compliance route; higher end of the HSFO band |
Two further points matter for procurement. First, MAN Energy Solutions/Everllence distinguishes "Category I" cylinder oils (Mark 8 and earlier) from "Category II" (Mark 9 and later, a tighter standard); BN 40 Category II is commonly cited as the mainstream low-sulphur grade for current-generation engines, but the applicable category depends on the specific engine mark, not the fuel alone. Second, mixing high-BN and low-BN cylinder oils, or running a high-BN oil continuously on low-sulphur fuel, is a recognized risk factor for excess unneutralized alkalinity and deposit formation — another reason not to standardize BN selection across a mixed fleet without checking each engine's current guidance.
How Do I Choose the Right BN Grade for a Specific Vessel? (Matching BN to Fuel and Engine NOL)
A defensible cylinder oil purchase decision runs through a short, repeatable checklist rather than a single lookup:
- Confirm the actual fuel sulphur content the vessel is burning — VLSFO/ULSFO under the 0.50% global cap, ECA-grade distillate at 0.10%, or HSFO on a scrubber-fitted vessel — rather than assuming from vessel type or trade route.
- Identify the engine maker, model, and Mark generation (for example, a specific MAN B&W or WinGD mark), since BN category and feed-rate guidance are issued per engine mark, not as one universal figure.
- Check the current engine maker service letter for that mark and fuel combination, rather than relying on an older letter or general trade-press guidance — engine makers revise this guidance periodically.
- Request the supplier's own dated No-Objection Letter (NOL) for the specific product being quoted (see the next section) — a BN claim alone is not the same as a current NOL.
- Request a batch-specific Certificate of Analysis (COA) for the actual drums or IBCs being shipped, not a representative or older COA (see the COA section below).
This sequence — fuel sulphur, engine mark, current service letter, supplier NOL, batch COA — mirrors the checks a ship management company's technical superintendent would run before authorizing a purchase order, and it is the information an RFQ needs to carry so a supplier can quote the correct grade.
What Is Cylinder Oil Feed Rate and Why Does It Matter?
Feed rate is the metered dose of cylinder oil injected per unit of engine output, expressed in grams per kilowatt-hour (g/kWh). Modern low-speed two-stroke engines use electronically controlled, load-dependent lubrication systems (such as the "Alpha"-type system referenced in MAN B&W engine documentation) that inject oil intermittently — timed to roughly every 2–20 engine revolutions — to hold a target g/kWh feed rate regardless of engine speed, an advantage over older, purely mechanical, speed-linked lubricators.
🟡 Multiple secondary trade sources report a commonly cited minimum feed-rate floor in the region of 0.60 g/kWh, with some guidance suggesting a rate as high as approximately 0.8 g/kWh on some later-mark engines running low-sulphur fuel, specifically to keep the piston and liner clean and avoid metal-to-metal contact. These figures were not independently confirmed against the primary engine maker service letter and should be treated as indicative rather than a fixed rule.
The safest buyer-facing principle does not depend on a single number: feed-rate optimization became a significant cost and emissions lever after IMO 2020, and engine makers issue periodic service-letter updates on it. Always check the current service letter for the specific engine mark rather than relying on a fixed g/kWh figure from an older document.
What Is a No-Objection Letter (NOL), and Why Does It Matter More Than "Meets the Spec"?
Engine makers do not license cylinder oils the way an automotive standards body licenses engine oils. Instead, MAN Energy Solutions/Everllence and WinGD each run their own service test and confirmation test protocol, and — if a specific formulation passes — issue a No-Objection Letter (NOL) stating that the maker has no objection to that specific supplier's specific product being used in its engines.
Two things follow directly from that process, and both matter to a buyer with engine-warranty exposure:
- "Meets the specification" is not the same claim as "holds a current, dated NOL." A product can be formulated to a published BN and viscosity specification without having completed a specific engine maker's test protocol. Ask the supplier for the actual NOL document, not just a BN or spec claim.
- An NOL is product- and formulation-specific. It does not transfer to another supplier's product with a similar BN claim, and it does not apply category-wide. A current NOL for one supplier's BN 40 oil says nothing about a different supplier's BN 40 oil.
Altonex Global does not issue, verify, or guarantee NOL status for any listing — the platform is the RFQ marketplace connecting buyers to suppliers, and each supplier remains solely responsible for its own NOL, specification, and compliance claims. Buyers who need engine-maker NOL coverage should request the supplier's current dated NOL document directly as part of the RFQ before placing an order, rather than relying on a general BN or "Category II" statement in a listing.
Cylinder Oil vs. System Oil — Why Are They Two Completely Different Products?
A two-stroke crosshead engine runs two entirely separate lubricating oil circuits, and the two products are not interchangeable:
- Cylinder oil — the total-loss lubricant discussed throughout this guide, injected directly at the liner wall and consumed with every stroke.
- System oil — circulates continuously through the main engine lube-oil pump to lubricate the crankcase bearings, crosshead, thrust bearing, and camshaft, and is not consumed in normal operation apart from minor leakage losses.
The separation exists so the crankcase circuit stays isolated from combustion by-products, which lets the engine burn a lower-quality, higher-sulphur fuel in the cylinder without contaminating the crankcase oil that lubricates the bearings and running gear. The two products carry different BN/TBN ranges and different viscosity duty, so specifying or storing one in place of the other is never a safe substitution. Buyers sourcing system oil for the same vessel should treat it as a separate specification and a separate RFQ line, not an extension of the cylinder oil order.
What Should Be on a Cylinder Oil Certificate of Analysis (COA)?
🟡 As standard industry TDS/COA practice, a batch-specific cylinder oil Certificate of Analysis typically reports:
- Kinematic viscosity at 100°C (KV100, cSt)
- Base Number (BN, mg KOH/g, per ASTM D2896)
- Flash point (°C, Cleveland open cup)
- Pour point (°C)
- Density at 15°C (kg/m³)
- Sulfated ash (%)
- Calcium content (ppm) — a proxy for detergent/additive treat rate
Always request the COA matching the actual batch or drum numbers being shipped, not a representative or older COA on file. For cylinder oil specifically, the COA should state the fuel-sulphur compatibility or BN grade clearly enough for the receiving vessel's engineers to confirm the correct product is aboard for the fuel currently being burned — a check that matters more here than for a generic industrial lubricant.
Who Buys Marine Cylinder Oil?
The B2B buyer set for marine cylinder oil is broader than a single vessel operator placing a one-off order. It typically includes:
- Shipowners and ship operators buying directly for their own fleet.
- Ship management companies, where technical superintendents procure on behalf of managed fleets across multiple owners.
- Bunker and lubricant traders or brokers who supply into specific ports on the buyer's behalf.
- Marine lubricant distributors and resellers holding local stock at bunkering hubs.
This describes market structure, not a fixed statistical split — the right buyer profile for a given RFQ depends on the vessel, the fleet's procurement model, and the port where delivery is needed.
What HS Code Applies to Marine Cylinder Oil Exports?
Marine cylinder oil is classified under HS 2710.19 at the internationally harmonized 6-digit level — "petroleum oils and oils obtained from bituminous minerals (other than crude); medium/heavy oils including lubricating oils." This 6-digit heading is consistent across customs jurisdictions worldwide.
🟡 Below the 6-digit level, classification is destination-specific. As one example, in the United States finished non-turbine lubricating oil (including a main-propulsion diesel engine's cylinder oil) is commonly classified at the 10-digit HTS subheading 2710.19.3020, while turbine lubricating oil sits in a separate 2710.19.3030 subheading — but 8- and 10-digit codes vary by destination country and are not internationally standardized. Every export shipment should have its destination-specific code confirmed by a licensed customs broker rather than relying on a code used for a previous shipment to a different country.
How Is Marine Cylinder Oil Packaged, and What MOQ Should I Expect?
🟡 Cylinder oil is predominantly shipped in 200 L / 208 L UN 1A1 closed-head steel drums, the standard format for shipboard bunkering compatibility; large fleet operators and blending or distribution hubs may instead order 1,000 L IBCs. Illustrative container-loading figures — always to verify against the supplier's actual specific gravity and packing method — run to roughly 80 palletized 200 L drums per 20-foot container (up to about 100 hand-loaded), or 10–20 x 1,000 L IBCs, weight-limited by specific gravity (typically SG 0.87–0.90 for mineral base oils; higher-BN oils may run denser).
🟡 Indicative export minimum order quantities reported across the marine lubricants trade run to roughly 20–50 drums per SKU for 208 L drums, or roughly 4–10 IBCs for 1,000 L IBCs. These are industry-typical ranges only — never a fixed Altonex Global or supplier-quoted figure — and the current MOQ for any specific product should always be confirmed directly with the supplier through an RFQ.
What Export Documents Does a Marine Cylinder Oil Shipment Require?
A standard marine cylinder oil export shipment is typically supported by:
- Commercial Invoice (stating HS 2710.19, Incoterms, and port of loading/destination)
- Packing List (drum or IBC counts, gross/net weights, batch numbers)
- Bill of Lading (an original is required for Letter of Credit transactions)
- Batch-specific Certificate of Analysis
- Safety Data Sheet in the GHS Rev. 9 (2021) 16-section format
- Certificate of Origin (where a preferential duty claim under a free trade agreement applies)
- Marine Cargo Insurance Certificate (under CIF/CIP terms)
Incoterms 2020 (effective 1 January 2020) governs cost and risk transfer between buyer and seller; FOB and CIF are the terms most commonly requested in marine lubricant B2B RFQs from emerging-market buyers. Under Incoterms 2020, FOB risk transfers when the goods are placed on board the vessel nominated by the buyer — the older "ship's rail" concept was removed in 2010 and no longer applies. Confirm the applicable Incoterm and the destination-specific HS subheading with the supplier and customs broker before shipment.
How Do I Request a Quote for Marine Cylinder Oil on Altonex Global?
Altonex Global is a B2B trade expo and RFQ marketplace connecting marine lubricant buyers with suppliers — the platform does not sell, stock, or ship cylinder oil itself, and is never the seller of record for any listing. To request a quote, a buyer should be ready to specify: product type (cylinder oil), target BN grade, the vessel's actual fuel type (VLSFO/ULSFO/HSFO/MGO/LNG), engine maker, model, and Mark generation, whether a current NOL is required, packaging format, indicative quantity, Incoterms and port of loading, the documents required (COA, SDS, Certificate of Origin), lead time, and payment terms.
Browse current listings on the Marine Cylinder Oils category on Altonex Global and submit a Request for Quote, Contact Supplier, or Export Inquiry with the specification above so a supplier can respond with the correct BN grade, current NOL status, and export terms for the vessel in question. For related sourcing guidance — including system oils, HS classification, and export documentation across other marine and industrial lubricant categories — visit the Altonex Global Knowledge Hub.