Key takeaways
- A steam cracker fed on ethane yields roughly 80% ethylene with minimal co-products, while a naphtha cracker yields only around 30–35% ethylene alongside propylene, C4s and pyrolysis gasoline — so the feedstock choice fixes both the cost and the entire product slate.
- Ethane is priced off natural gas (Henry Hub in the US, or low-netback associated gas in the Gulf states), whereas naphtha tracks crude oil; when the oil-to-gas ratio is wide, ethane crackers in the US Gulf and the Gulf states sit at the bottom of the global cost curve and naphtha crackers in Northeast Asia and Europe set the marginal price.
- Naphtha's co-product credit is decisive: a naphtha cracker only competes when propylene, butadiene and benzene values are strong enough to offset its higher feed cost, which is why integrated producers run cracker margins net of co-product credits rather than on ethylene alone.
- Propylene and butadiene supply are structurally tied to naphtha cracking and refinery FCC units, so a global shift toward ethane and on-purpose PDH economics tightens propylene relative to ethylene — a divergence buyers read directly in the PP-versus-PE price spread.
Every polyethylene number you are quoted starts at the cracker, and the cracker starts with a feedstock decision: gas or liquid. That single choice — ethane versus naphtha — fixes how much ethylene a plant makes per tonne of feed, what else comes out alongside it, what the feed costs, and ultimately where a producer sits on the global cost curve. Understand the feedstock split and most regional price gaps stop looking arbitrary and start looking like arithmetic.
This is the layer beneath the headline grade. When you compare a Gulf HDPE offer against a Northeast Asian one, you are mostly comparing ethane against naphtha. The resin can be identical on the certificate of analysis; the cost base is not. For how those costs reach your invoice, pair this with our note on how polymer pricing works.
A steam cracker heats a hydrocarbon feed to roughly 800–850°C in the presence of steam, breaking long molecules into shorter, reactive ones — principally ethylene and propylene, the two building-block olefins. The feed determines the product mix. Light feeds (ethane, propane) crack cleanly to ethylene. Heavy feeds (naphtha, gasoil) crack into a broad spread of products because they contain a wider range of molecules to begin with.
Ethane is a natural gas liquid — C₂H₆, two carbons. Naphtha is a light refined cut, broadly C₅–C₁₂, drawn off crude oil distillation. That structural difference is the whole story: a two-carbon feed has nowhere to go but ethylene, while a five-to-twelve-carbon feed fragments into ethylene, propylene, a C4 stream and aromatics. Yield and slate follow directly from carbon number.
The figures below are typical, route-defining yields — actual plant numbers vary with cracking severity and design, but the shape holds everywhere. The key point: an ethane cracker is an ethylene machine, while a naphtha cracker is a multi-product refinery in miniature.
| Product | Ethane cracker | Naphtha cracker |
|---|---|---|
| Ethylene | ~80% | ~30–35% |
| Propylene | ~2–3% | ~14–17% |
| C4 stream (incl. butadiene) | low | ~9–11% |
| Pyrolysis gasoline (aromatics: benzene, toluene) | minimal | ~18–24% |
| Fuel gas / other | balance | balance |
| Co-product credit to ethylene cost | negligible | significant |
Read the table as economics, not chemistry. The ethane cracker makes one valuable thing and little else, so its cost per tonne of ethylene is essentially feed-plus-energy. The naphtha cracker makes ethylene plus a stream of saleable co-products — propylene for polypropylene, butadiene for synthetic rubber, benzene and toluene for the aromatics chain. Those co-product sales subsidise the ethylene. A producer's true cracker margin is calculated net of co-product credits, which is why a naphtha cracker can compete when downstream propylene and aromatics markets are strong, and struggles when they are weak.
An ethane cracker bets on cheap gas; a naphtha cracker bets on its co-products. The buyer pays for whichever bet is winning that month.
Feedstock cost is set in two different markets. Ethane is priced off natural gas — Henry Hub in the US, or low-netback associated gas in the Gulf states, where ethane has historically been allocated to crackers at advantaged prices. Naphtha is priced off crude oil, trading at a spread to Brent or the relevant marker. So the contest between routes is, at root, a contest between the gas complex and the oil complex.
The single most useful ratio to watch is oil-to-gas. When crude is expensive relative to natural gas — a wide oil-to-gas ratio — ethane crackers enjoy a deep cost advantage and naphtha crackers are squeezed. When the ratio narrows, the advantage erodes and naphtha's richer co-product slate can claw back competitiveness. This is why two crackers making the identical molecule can carry feed costs that differ by a wide margin depending purely on the energy backdrop.
- Ethane (gas-linked): narrow slate, ~80% ethylene, low energy and capital intensity per tonne — advantaged when gas is cheap versus oil.
- Naphtha (oil-linked): broad slate, ~30–35% ethylene, high co-product credit — advantaged when propylene, butadiene and aromatics are strong, or when the oil-to-gas ratio narrows.
- Marginal producer sets the price: in a balanced market, the highest-cost tonne needed to meet demand — usually a naphtha cracker in Asia or Europe — sets the clearing ethylene price, so low-cost ethane producers capture the spread as margin.
Stack the world's crackers from lowest cash cost to highest and you get the global cost curve. The bottom is dominated by Middle East ethane and US Gulf Coast ethane, the latter fed by abundant shale gas liquids. The top is Northeast Asian and European naphtha crackers, which carry the oil-linked feed cost and must lean on co-products to stay in the game. Demand draws the line: the marginal cracker required to balance the market sets the price, and everyone below it earns the difference.
| Region | Primary feedstock | Cost-curve position | What drives their economics |
|---|---|---|---|
| Middle East (Gulf) | Ethane (low-cost gas) | Bottom | Advantaged feed allocation; export-oriented PE |
| US Gulf Coast | Ethane (shale NGLs) | Low | Cheap domestic gas; flexible light feeds |
| Northeast Asia | Naphtha | High / marginal | Oil-linked feed; relies on co-product credits |
| Europe | Naphtha | High / marginal | Oil-linked feed plus higher energy and carbon costs |
This is the structural reason that Middle East origin polyethylene and US material tend to undercut Asian offers on a like-for-like grade. It is not a quality difference — ethylene is C₂H₄ wherever it is made, and the finished resin meets the same density (ISO 1183) and melt flow (ISO 1133 / ASTM D1238) specifications. It is a feedstock difference, capitalised into the cost base. For grade definitions across the PE family, see our HDPE, LDPE and LLDPE primer.
There is a sting in the tail for anyone buying polypropylene. Propylene is overwhelmingly a co-product — of naphtha cracking and of refinery FCC units — rather than a primary output of ethane crackers. As the world has shifted toward cheap ethane and dedicated on-purpose routes such as propane dehydrogenation (PDH), the supply of propylene relative to ethylene has tightened. The practical effect: when ethane is cheap and PE softens, propylene and PP do not necessarily follow, because their feedstock chain is different.
That makes the PP-to-PE price spread a live signal of feedstock economics rather than just relative demand. A widening PP premium often reflects propylene scarcity driven by the gas-versus-oil shift, not a sudden surge in PP consumption. Buyers who track both monomers — and who read the 2026 market outlook with feedstock in mind — anticipate these moves instead of reacting to them.
Feedstock prints are a leading indicator, not a same-day pass-through. Contract PE and PP settle monthly and reference monomer movements with a lag of weeks; spot offers react faster. Watch three things: the oil-to-gas ratio (direction of the cost-curve advantage), the co-product complex (butadiene and aromatics strength, which sets how hard naphtha crackers can fight), and the PP–PE spread (the cleanest read on propylene scarcity). When the desk frames an offer, this is the chain we price backward from — and it is the same logic that should sit behind your next RFQ. To put it to work on origin and term, talk to the OmniaStrata desk via our contact page or review the polyethylene sourcing service.
The takeaway is simple to hold and hard to overstate: you are never really buying resin in isolation — you are buying a position on the cost curve. Knowing whether your supplier cracks gas or liquid, and where the oil-to-gas ratio sits, tells you more about your next quote than any single spot index will. Price the feedstock, and the resin price stops surprising you.
Frequently asked
Questions on the desk
Why is Middle East and US polyethylene usually cheaper than Asian material?
Both regions crack ethane, a gas-based feedstock priced off relatively cheap natural gas rather than crude oil. Ethane crackers convert roughly 80% of feed to ethylene with low energy and capital intensity per tonne, putting Gulf and US Gulf Coast producers near the bottom of the global cost curve. Asian crackers run naphtha, which is oil-linked and far more expensive per tonne of ethylene, so they typically set the marginal — and therefore the highest — cost of supply.
Does the feedstock affect the quality of the polymer I receive?
No. Ethylene is ethylene (C₂H₄) regardless of whether it came from ethane or naphtha, so the resulting HDPE, LLDPE or LDPE meets the same specifications and the same test standards — density per ISO 1183, melt flow per ISO 1133 / ASTM D1238. Feedstock affects cost, availability and which co-products a producer can offer, not the resin's intrinsic properties. Always verify a grade against its certificate of analysis, not the cracker route.
Why do polypropylene prices sometimes move opposite to polyethylene?
Propylene is mostly a co-product of naphtha cracking and refinery FCC units, not of ethane cracking. As more of the world's ethylene comes from ethane and on-purpose PDH routes, propylene supply tightens relative to ethylene. When ethane is cheap, PE can soften while PP holds firm because its feedstock chain is different — so the PP–PE spread is a useful read on feedstock economics, not just demand.
What is the co-product slate and why should a buyer care?
A naphtha cracker produces a mix — ethylene, propylene, a C4 stream (butadiene), and pyrolysis gasoline rich in benzene. The combined value of those co-products subsidises the ethylene cost, so a producer's real cracker margin is calculated net of co-product credits. When butadiene and aromatics are weak, naphtha-based ethylene effectively gets more expensive, which can lift PE offers even when oil prices have barely moved.
How quickly do feedstock cost changes show up in resin offers?
Contract polyethylene and polypropylene are usually settled monthly and reference monomer or feedstock movements with a lag of weeks, not days; spot offers react faster. A sharp move in crude or natural gas signals a directional shift, but the size and timing depend on monomer contract mechanics, inventory positions and co-product values. Treat feedstock prints as a leading indicator, not a same-day pass-through.
General market commentary from the OmniaStrata desk, provided for information only. It is not legal, financial, tax, or trading advice, and it is not an offer or a commitment to any terms. Figures such as price ranges, spreads, financing costs, and credit periods are illustrative market context, not OmniaStrata's rates or terms. Actual contract terms — including price, payment instrument, credit, insurance, and Incoterms — are agreed in writing on a per-transaction basis and at OmniaStrata's discretion. Market conditions change; figures reflect the publication date.