Every oil well in the world produces it. In some basins, it is worth more than the oil itself. In others, it is flared into the atmosphere at a rate of hundreds of millions of cubic feet per day.
Associated gas — the natural gas that is dissolved in crude oil and released when oil reaches the surface — is one of the most commercially significant and operationally complex byproducts of oil production.
For upstream operators, associated gas represents both an opportunity and a challenge. Handled correctly, it is a fuel source, a revenue stream, and a tool for improving overall field economics. Handled poorly — or not at all — it becomes a flared waste product, a regulatory liability, and a direct cost to investors through lost hydrocarbon value.
Understanding what associated gas is, where it comes from, and what options operators have to capture and use it is essential for any engineer, operator, or investor working in upstream oil and gas.
What Is Associated Gas?
Associated gas (also called associated petroleum gas, or APG) is natural gas that is produced alongside crude oil from an oil well.
It exists in two primary forms:
Dissolved gas is gas that is dissolved directly in the crude oil under reservoir pressure, similar to how carbonation is dissolved in a carbonated beverage. When pressure drops as oil moves from the high-pressure reservoir to the low-pressure surface, the dissolved gas comes out of solution — just like carbonation escaping when you open a bottle.
Gas cap gas exists in a free gas phase in a structural trap directly above the oil column in a reservoir. As the reservoir is produced, this gas cap gas may be produced through the well along with the oil.
Both forms of associated gas must be separated from the crude oil at surface facilities before the oil can be stored, transported, or sold.
Where Does Associated Gas Come From?
The concentration and composition of associated gas depends on the reservoir characteristics, the depth and pressure of the formation, and the oil’s API gravity.
Light, high-API crude oils typically contain more dissolved gas than heavier crudes. Deep, high-pressure formations release more gas at surface than shallow formations. Shale oil plays like the Permian Basin’s Wolfcamp and the Bakken in North Dakota are particularly gassy — producing large volumes of rich associated gas alongside every barrel of crude.
This is why some of the largest flaring volumes globally occur in exactly the same basins producing the most oil.
What Is the Gas-Oil Ratio (GOR)?
The Gas-Oil Ratio (GOR) measures how much associated gas a well produces relative to its crude oil output.
GOR is expressed as standard cubic feet of gas per barrel of oil (scf/bbl) or thousand cubic feet per barrel (Mcf/bbl).
- Low GOR: below 500 scf/bbl — relatively little associated gas per barrel
- Moderate GOR: 500–2,000 scf/bbl — significant gas volumes
- High GOR: above 2,000 scf/bbl — very high gas relative to oil
A well producing 500 barrels per day at 2,000 scf/bbl GOR generates 1 MMscfd of associated gas. That is enough to power multiple large generators or supply a full frac fleet with fuel.
High-GOR wells represent the greatest opportunity — and the greatest operational pressure — for associated gas management.
The Composition of Associated Gas
Associated gas is not pure methane. It is a mixture of hydrocarbons and other components whose exact proportions vary by formation and reservoir conditions.
Typical associated gas composition from a shale oil play includes:
| Component | Typical Range |
|---|---|
| Methane (C1) | 50–75% |
| Ethane (C2) | 8–15% |
| Propane (C3) | 5–12% |
| Butanes (C4) | 3–8% |
| Pentanes+ (C5+) | 2–6% |
| CO₂, N₂, H₂S | Variable |
The heavy hydrocarbon content — propane, butanes, and natural gasoline — gives associated gas from oil wells a significantly higher BTU value than lean pipeline-quality natural gas. It also makes raw associated gas unsuitable for use in gas engines without conditioning — the heavy components lower the Methane Number below what engines can safely combust.
How Is Associated Gas Separated from Crude Oil?
At the surface, crude oil and associated gas are separated using production separators — pressure vessels that allow gas to flash off and be collected as the crude flows through progressively lower pressure stages.
Most upstream facilities use a two-stage or three-stage separation process:
- High-pressure separation removes the bulk of the gas
- Low-pressure separation removes additional lighter components
- Storage tanks capture final flash gas as crude enters atmospheric storage
Each stage produces a gas stream that must be handled — captured, combusted, or vented.
What Happens to Associated Gas After Separation?
Associated gas leaving a production separator can be managed in several ways, depending on infrastructure, economics, and regulatory requirements.
Gas Gathering and Pipeline Sales
Where gathering infrastructure exists and the gas meets pipeline specifications, associated gas can be compressed and injected into a gathering system for sale to a midstream processor. This is the preferred outcome, but requires pipeline access and gas that meets the gathering company’s composition requirements.
Flaring
Operators flare associated gas when they cannot capture it for sale or use. The gas is combusted in a flare stack, destroying hydrocarbon value and producing CO₂ emissions. Flaring is heavily regulated and increasingly restricted.
Venting
Direct venting releases unburned associated gas to atmosphere. This is the worst environmental outcome — methane is a potent greenhouse gas — and is prohibited except in emergency situations in most regulatory jurisdictions.
Reinjection
Some operators reinject associated gas back into the reservoir for pressure maintenance or enhanced oil recovery. This requires compression equipment and suitable reservoir conditions.
On-Site Utilization
The most economically attractive option in many situations: capture and condition the associated gas, then use it as fuel for generators, compressors, frac fleets, or other on-site energy needs — or process it to recover NGLs for sale.
Why Is Associated Gas Flared at Such Scale?
Despite its value, billions of cubic feet of associated gas are flared globally every day. The reasons include:
Infrastructure lag — oil production in new plays often outpaces gathering pipeline construction. Operators begin producing before gas capture infrastructure is available.
Out-of-spec gas — gathering systems have composition requirements. Gas too rich in heavy components, too high in CO₂ or H₂S, or too variable in composition may be rejected.
Small volume — at many smaller facilities, the gas volumes may appear too small to justify dedicated infrastructure under traditional models.
Remote location — some production is too geographically remote to connect to gathering economically.
Modern modular field gas conditioning systems have fundamentally changed the economics of on-site gas utilization for all of these situations — particularly the last three.
The Case for Capturing and Conditioning Associated Gas
Historically, the question was simply “can we get this gas to market?” Today, the more sophisticated question is: what is the highest-value use of this associated gas given the specific conditions of our operation?
The options, roughly in increasing value:
- Flare or vent — zero value, regulatory and ESG liability
- Sell into gathering as raw gas — commodity gas pricing, subject to pipeline specs and fees
- Use as on-site fuel after conditioning — displaces diesel, typically worth $3–$6/Mcf equivalent in fuel cost savings
- Recover NGLs + use residue as fuel — NGL liquids pricing (2–4x gas BTU value) plus fuel offset
The right answer depends on gas composition, GOR, available infrastructure, and on-site energy demand. Pioneer Energy’s engineering team routinely evaluates all four options using a HYSYS-based process model of the customer’s actual gas composition data.
From Liability to Asset: How Modular Systems Change the Math
The transformation in associated gas economics over the past decade has been driven by modular, skid-mounted field gas conditioning technology.
Systems like Pioneer Energy’s Pegasus product family are designed specifically for this challenge:
- Deployed at remote wellsites without permanent plant construction
- Handle wide ranges of gas composition, GOR, and inlet pressure
- Condition raw associated gas to consistent, on-spec fuel quality
- Optionally recover Y-grade NGLs from the heavy hydrocarbon fraction
- Cloud-enabled controls with remote monitoring and autonomous operation
The Pegasus Dream — Pioneer’s highest-capacity system at up to 4 MMscfd — is designed for large, high-GOR production facilities where significant associated gas volumes need to be handled reliably. The Pegasus LP covers flows up to 2 MMscfd and is one of the most widely deployed associated gas conditioning systems in the field today.
For operations where associated gas volumes vary significantly — common in multi-well pads where production rates fluctuate — Pioneer’s building-blocks approach allows multiple units to be paralleled or reconfigured as the operation evolves.
Associated Gas and Upstream Emissions
The scale of associated gas flaring is one of the largest preventable methane emission sources in the energy sector. The World Bank estimates that approximately 140 billion cubic meters of gas are flared annually — representing roughly 400 million tonnes of CO₂-equivalent emissions.
For oil producers, reducing associated gas flaring is no longer optional in most major producing jurisdictions. EPA rules, state-level regulations from the COGCC, NMOCD, and others, and ESG commitments from major operators and institutional investors all demand measurable progress on flare reduction.
The practical path to flare reduction is the same as the path to associated gas monetization: capture it, condition it, and use it.
Conclusion
Associated gas is an inseparable part of oil production. How operators handle it — whether they flare it, vent it, or capture and monetize it — has significant consequences for project economics, regulatory compliance, and environmental performance.
Modular field gas conditioning systems from Pioneer Energy make on-site associated gas utilization practical at a much wider range of facilities than was possible under previous-generation technology. Whether the goal is generating on-site power, supplying fuel gas to a frac fleet, or recovering Y-grade NGLs for truck-out, the path starts with conditioning the associated gas stream.
Contact Pioneer Energy’s engineering team to evaluate the associated gas volumes and composition at your facility and determine the highest-value utilization pathway for your specific operation.
Frequently Asked Questions
What is associated gas in oil production?
Associated gas (also called associated petroleum gas or APG) is natural gas that is dissolved in crude oil or exists in a gas cap directly above an oil reservoir. It is produced alongside crude oil and must be handled — captured, flared, vented, or injected — before the crude can be stored and sold.
What is the difference between associated gas and non-associated gas?
Associated gas comes from oil wells and is produced alongside crude oil. Non-associated gas comes from dedicated gas wells where natural gas is the primary product. Associated gas often has higher concentrations of heavier hydrocarbons (propane, butane, natural gasoline) compared to pipeline-quality non-associated gas.
Why is associated gas flared instead of captured?
Operators flare associated gas when no gathering pipeline exists, when gathering capacity is full, when gas composition is outside pipeline specifications, or when the economics of capture have historically not justified the infrastructure cost. Modern modular conditioning systems have significantly changed the capture economics.
What is the GOR in oil production?
GOR stands for Gas-Oil Ratio. It is the ratio of produced gas to produced oil, expressed in standard cubic feet of gas per barrel of oil (scf/bbl). High-GOR wells produce large volumes of associated gas relative to crude oil and represent the greatest opportunity for gas capture and monetization.
What can associated gas be used for?
Conditioned associated gas can be used as fuel for on-site generators, compressors, heater treaters, and frac fleets; injected into gas gathering pipelines; processed to recover Y-grade NGLs; compressed for CNG; or used as gas lift gas to boost production from declining wells.
How does field gas conditioning treat associated gas?
Field gas conditioning systems remove the heavy hydrocarbons (propane, butane, pentanes), free liquids, water vapor, and other contaminants from raw associated gas, raising the Methane Number and producing a clean, consistent gas stream suitable for use as fuel or pipeline injection.