Natural Gas Liquids (NGLs): What They Are, How They’re Priced, and Why They Matter

Natural gas liquids defined Natural gas liquids (NGLs) are hydrocarbon compounds — primarily ethane, propane, butane, isobutane, and pentane — that are extracted from the natural gas stream at gas processing plants. They are heavier than methane and can be separated and liquefied for individual sale. NGLs are distinct from LNG (which is methane) and closely related to LPG (propane and butane are a subset of NGLs). The US Permian Basin and Marcellus Shale are the world’s dominant NGL-producing regions, priced at Mont Belvieu, Texas.

Table of Contents

1. What NGLs Are and How They Differ from LNG and LPG
2. The Five NGL Components and What Each Is Used For
3. How NGLs Are Separated from Natural Gas
4. Where NGLs Come From: US Dominance
5. The Two Key US Pricing Hubs: Mont Belvieu and Conway
6. Seasonal Demand Curves
7. The Y-Grade, Purity, and Fractionation Spread
8. Frequently Asked Questions
9. Key Takeaways

What NGLs Are and How They Differ from LNG and LPG

The naming conventions in the gas industry are genuinely confusing. Let us untangle them.

Natural gas from a well is not pure methane. It contains methane (roughly 70–90%) plus smaller amounts of ethane, propane, butane, isobutane, and pentane. It also contains non-hydrocarbons: CO2, nitrogen, and hydrogen sulphide.

The heavier hydrocarbon components — ethane through pentane — are the natural gas liquids. They are called “liquids” because, unlike methane, they can be liquefied at relatively mild conditions (moderate pressure or mild cooling) and handled as liquids in pipelines and storage tanks.

The distinction from LNG and LPG:

• LNG = liquefied natural gas = primarily methane, cooled to −162°C for ocean transport. LNG is not an NGL.
• LPG = liquefied petroleum gas = propane and butane used as commercial fuels. LPG is a subset of NGLs — all LPG components are NGLs, but ethane and pentane-plus are also NGLs without being LPG.
• NGLs = the full family of heavier hydrocarbon components extracted from natural gas, of which propane and butane (LPG) are just two members.

Product	Main component	Relationship to NGLs
Natural gas (pipeline)	Methane (CH4)	Not an NGL
LNG	Methane (cooled to −162°C)	Not an NGL
Ethane	C2H6	NGL — not LPG
LPG (propane + butane)	C3H8 + C4H10	NGL subset
Pentane-plus / natural gasoline	C5+	NGL — not LPG

The Five NGL Components and What Each Is Used For

Each NGL component is a distinct commodity with its own market, pricing, and end-use sector.

Ethane (C2H6)

Ethane is the lightest NGL. It is almost exclusively used as a petrochemical feedstock — fed into steam crackers that break it into ethylene (C2H4), the most important petrochemical building block. Ethylene feeds production of polyethylene plastic (the most widely produced plastic globally), ethylene glycol (antifreeze, polyester), and many other derivatives.

The US Gulf Coast became the global centre of ethane-based ethylene production, built on cheap Permian and Marcellus ethane. US ethane is also exported by specialised very large ethane carriers (VLECs) to European and Asian steam crackers — a trade that grew substantially after 2016.

Propane (C3H8)

Propane is the most versatile NGL. Its end uses include:

• Residential and commercial heating (the “LP gas” in rural areas without natural gas pipelines)
• Autogas (vehicle fuel in many countries, particularly Turkey, South Korea, Poland)
• Petrochemical feedstock (propane dehydrogenation, or PDH, produces propylene for polypropylene plastic)
• Agricultural grain drying (a major seasonal use in the US Midwest)

Propane accounts for roughly 30% of total US NGL production by volume.

Normal Butane (C4H10) and Isobutane (C4H10)

Butane and isobutane have the same molecular formula but different structures and uses:

• Normal butane is blended into winter-grade gasoline (it has high vapour pressure that helps cold-weather starting). Refineries reduce butane in summer blends due to RVP regulations.
• Isobutane is a feedstock for alkylate production (a high-octane, clean-burning gasoline component) and for propylene oxide synthesis.
• Both are used in lighters and aerosol propellants at smaller volumes.

Pentane-plus (C5+ / Natural Gasoline)

Pentane and heavier components are liquid at room temperature. Their primary uses:

• Gasoline blendstock at refineries
• Diluent for heavy oil: Canadian oil sands producers use pentane-plus to thin bitumen for pipeline transport to refineries
• Naphtha-based petrochemical feedstock

How NGLs Are Separated from Natural Gas

NGL extraction and separation happens in two stages.

Stage 1: Gas processing plant (extraction)

At a gas processing plant near the wellhead, raw natural gas is treated to remove impurities and extract the NGL components. The NGLs come out as a mixed stream called Y-grade or raw mix — ethane, propane, butane, isobutane, and pentane all together in one liquid stream. Y-grade is typically transported by pipeline to a fractionation facility.

Stage 2: NGL fractionator (separation into purity products)

At a fractionation facility, Y-grade is separated into individual purity NGL streams through a series of distillation columns, each operating at different temperatures and pressures:

1. Deethaniser — removes ethane from the top
2. Depropaniser — removes propane from the remaining stream
3. Debutaniser — separates butane fraction from pentane-plus
4. Butane splitter — separates normal butane from isobutane
5. Pentane-plus remains at the bottom

The resulting purity products (specification ethane, specification propane, and so on) are stored and sold individually. The largest NGL fractionation complexes in the US are in Mont Belvieu, Texas.

The frac spread

The economic relationship between Y-grade NGL value and the individual purity product values is the fractionation spread (frac spread). If the combined value of separated purity products exceeds the value of Y-grade plus the cost of fractionation, it is economic to separate. If not, some processors may leave NGLs in the natural gas stream — a choice called ethane rejection — and sell everything as higher-BTU pipeline gas.

Where NGLs Come From: US Dominance

The United States produces approximately 60–65% of world NGL supply — a dominance built on the shale revolution.

Permian Basin (West Texas and New Mexico)

The Permian produces enormous volumes of associated gas — natural gas that emerges with crude oil from tight rock formations. Associated gas from the Permian has high NGL content, making each barrel of oil production a significant NGL generator as well. Permian crude oil production grew from roughly 2 million barrels/day in 2016 to over 5 million barrels/day by 2023, dragging NGL volumes up proportionally.

Marcellus and Utica (Pennsylvania, West Virginia, Ohio)

These Appalachian shale formations have a “wet gas window” — particularly in southwestern Pennsylvania and West Virginia — that produces significant ethane, propane, and butane alongside methane. Antero Resources, EQT, and Range Resources are major Appalachian NGL producers.

DJ Basin (Colorado), Bakken (North Dakota), Eagle Ford (Texas)

These basins contribute meaningful additional NGL volumes. The DJ Basin (Weld County, Colorado) produces high-NGL-content gas from Wattenberg field operators including Civitas Resources and Chevron.

Outside the US, the Middle East (Saudi Arabia, UAE, Qatar), Canada (Alberta), and Russia are significant NGL producers. The US shale revolution, however, made the US the global swing supplier of propane and ethane and gave the US LPG and NGL export capacity that did not exist before 2012.

The Two Key US Pricing Hubs: Mont Belvieu and Conway

NGL prices in the US are quoted at two main physical hubs.

Mont Belvieu, Texas

Mont Belvieu is 25 miles east of Houston and is the world’s most important NGL pricing hub. It houses the largest NGL storage and fractionation complex in the world — underground salt caverns storing tens of millions of barrels of ethane, propane, butane, and pentane-plus. Enterprise Products Partners, Targa Resources, and MPLX operate major Mont Belvieu facilities.

NGL purity products at Mont Belvieu are priced in cents per gallon by component. Prices are published daily by Argus Media and OPIS (Oil Price Information Service). Propane at Mont Belvieu is sometimes also quoted as a percentage of WTI crude oil price — “propane as a percent of crude” is a standard market reference.

Most US NGL export terminals (Enterprise’s Morgan’s Point, Targa’s Galena Park) are near Mont Belvieu, making it the natural hub for NGL export pricing as well.

Conway, Kansas

Conway is the secondary hub serving the Midcontinent production region (Oklahoma, Kansas, Colorado). It typically trades at a discount to Mont Belvieu reflecting transportation costs to reach Gulf Coast markets and export terminals.

The Conway-Belvieu differential is a closely watched spread. When Midcontinent production runs ahead of pipeline takeaway capacity to Mont Belvieu, Conway prices fall relative to Belvieu. Pipeline expansions over the 2010s generally narrowed this differential for propane and butane, though it periodically widens again when new production exceeds infrastructure.

Seasonal Demand Curves

NGL prices — particularly propane — follow strong seasonal patterns.

Propane: winter heating demand

Propane is the primary heating fuel for millions of US rural households without access to natural gas pipelines. Heating demand peaks sharply from November through February. Propane prices typically rise from late summer (as the market anticipates winter demand and distributors build inventories) and fall from spring through summer (as inventories are replenished and demand drops).

The EIA (US Energy Information Administration) publishes weekly US propane/propylene inventory data — a market-moving report in winter. Inventories significantly below the five-year average entering winter can trigger propane price spikes. The 2013–14 winter (the “polar vortex”) caused propane prices to spike above $5/gallon in parts of the US Midwest due to a combination of high heating demand and logistical constraints in moving propane from storage to rural distributors.

Butane: gasoline blending seasons

Normal butane blending into gasoline is subject to seasonal RVP (Reid Vapour Pressure) regulations. In winter, higher RVP is permitted and refineries blend more butane into gasoline. In summer, RVP limits fall. This creates a “butane blending season” that begins in autumn (October–November) and ends in spring. Butane prices typically rise ahead of the blending season and fall as summer approaches.

Ethane: relatively flat seasonality

Ethane demand from steam crackers running continuously is relatively steady through the year. Seasonal fluctuations in ethane price reflect more about cracker feedstock economics (ethane vs. propane vs. naphtha cracking margins) and outages than end-use demand cycles.

The Y-Grade, Purity, and Fractionation Spread

For analysts tracking NGL markets, the relationship between Y-grade and purity products is fundamental.

Y-grade (raw mixed NGL) trades at a blended value reflecting its composition and current purity product prices. A Y-grade barrel rich in propane and butane will trade above a barrel heavy in ethane, because ethane is lower-valued in most environments.

Midstream companies — Enterprise Products Partners, Targa Resources, MPLX, DCP Midstream (now part of Phillips 66) — gather Y-grade from producers, transport it to fractionation facilities, and separate it into purity products. They earn either a fixed fee per gallon processed or a share of NGL value (keep-whole contracts).

Ethane recovery vs. ethane rejection

Producers and processors decide how much ethane to extract versus leave in the pipeline gas stream. When ethane prices are below the energy value of leaving ethane in the gas (as methane-equivalent BTU content), the economic choice is “ethane rejection” — leave it in the gas and sell it as fuel. When ethane prices are high relative to gas (typically when ethylene demand is strong), “ethane recovery” maximises revenue.

Ethane rejection materially affects ethylene supply. When US producers reject ethane on a large scale, less feedstock is available for steam crackers, which can tighten ethylene supply and support petrochemical prices.

Frequently Asked Questions

What is the difference between wet gas and dry gas?

Wet gas is natural gas with significant NGL content — high percentages of ethane, propane, and heavier hydrocarbons. Dry gas is nearly pure methane with minimal NGL content. Wet gas areas (such as the Marcellus wet gas window in southwestern Pennsylvania) produce valuable NGL byproducts alongside methane. Dry gas areas (such as the core Haynesville Shale in Louisiana) produce primarily pipeline-quality methane. Producers generally prefer wet gas because NGL revenues supplement gas revenue, improving well economics.

Why does ethane sometimes have a very low or negative price?

When NGL production runs ahead of fractionation capacity or pipeline takeaway, ethane prices can fall close to zero at stranded locations. When ethane is worth less than its equivalent value as pipeline gas BTU content, processors reject ethane — leaving it in the gas stream. This depresses the gas stream’s quality slightly but avoids the cost of moving a low-value commodity. Ethane traded near zero or below at Conway and some Appalachian locations during the mid-2010s Marcellus production surge.

How does the Henry Hub natural gas price affect NGL prices?

Natural gas prices set a floor of sorts for NGLs in some applications — NGLs compete with natural gas as a heating fuel. When gas prices rise, propane becomes relatively more competitive, supporting propane demand and price. However, ethane’s price is more closely tied to ethylene margin economics than to Henry Hub. Higher gas prices also reduce the incentive for ethane rejection, since the energy-equivalent value of leaving ethane in the gas stream rises with gas prices.

What are US NGL exports and why did they grow so quickly after 2015?

The US shale boom generated far more propane and butane than domestic markets could absorb. US propane exports grew from near-zero in 2012 to over 1.5 million barrels per day by 2020 — primarily to Asian buyers (China, Japan, South Korea, India) and European petrochemical companies. Export terminals at Marcus Hook (Pennsylvania), Nederland (Texas), and Morgan’s Point (Texas) handle most US NGL exports. Ethane exports also grew as European and Asian steam crackers invested in equipment to run US ethane feedstock.

Which companies dominate US NGL midstream?

Enterprise Products Partners (EPD) is the largest NGL midstream company by any measure — operating the largest fractionation complex at Mont Belvieu, the largest NGL pipeline network, and significant NGL export capacity. Targa Resources, Williams Companies, MPLX (Marathon Petroleum), DCP Midstream (now part of Phillips 66), and Crestwood Equity Partners are other major players. On the production side, Pioneer Natural Resources, ConocoPhillips, and Diamondback Energy (Permian) and Antero Resources (Marcellus) generate the largest producer NGL volumes.

How do NGL prices affect oil production economics?

In oil basins where associated gas is produced alongside crude (Permian, Bakken, Eagle Ford), NGL revenue from that associated gas adds significant value per barrel of oil produced. When propane and ethane prices are high, the total economics of a Permian well — crude revenue + gas revenue + NGL revenue — are meaningfully better than when NGLs are depressed. NGL price collapses (as in 2019–20) noticeably reduce Permian well returns, moderating drilling activity even when crude prices themselves are adequate.

Key Takeaways

• Natural gas liquids (NGLs) are ethane, propane, butane, isobutane, and pentane — the heavier hydrocarbon components extracted from natural gas at gas processing plants.
• LPG (propane and butane) is a subset of NGLs; ethane and pentane-plus are also NGLs but not LPG. LNG (methane) is not an NGL at all.
• Each NGL component has a distinct end use: ethane → ethylene/plastics; propane → heating/autogas/petrochemicals; butane → gasoline blending; pentane-plus → gasoline blendstock and bitumen diluent.
• NGLs are separated from the natural gas stream as a mixed Y-grade stream, then fractionated into purity products at facilities concentrated at Mont Belvieu, Texas.
• Mont Belvieu, Texas is the world’s most important NGL pricing hub; Conway, Kansas serves the Midcontinent as a secondary benchmark. Both publish daily purity product prices.
• The US produces approximately 60–65% of world NGL supply, dominated by the Permian Basin and Marcellus Shale regions, with the US as the world’s leading NGL exporter.
• Propane prices follow strong seasonal patterns — rising into winter heating demand and falling in spring — making EIA weekly propane inventory data a key market indicator.
• The fractionation spread (value of purity products minus Y-grade value and processing cost) determines how aggressively midstream operators extract NGLs, including the key decision of ethane recovery versus ethane rejection.

Related Reading

To deepen your understanding of the topics covered in this article, explore these related guides: the downstream products that compete in heating and transport fuel markets, the upstream operations where associated gas is often co-produced and how biofuel blending mandates compete with NGL-derived gasoline components.