A processing plant recovers one commingled stream of natural gas liquids from gas that many producers delivered, and it has to divide those actual barrels fairly among them. The standard method starts by estimating how many liquids each producer's gas theoretically contained, then scales those estimates down to match what the plant really recovered. This guide explains how theoretical yield is computed from gas composition and volume, why theoretical never quite equals actual, and how the yield-to-actual factor turns estimates into the real barrels each producer is paid for.
NGL Theoretical Yield in one line: NGL theoretical yield allocation estimates each producer's liquids share by multiplying the gas composition - expressed as gallons of each recoverable component per thousand cubic feet, or GPM - by the metered gas volume, giving a theoretical barrel figure per producer. Because plants never recover exactly what theory predicts, those theoretical yields are then scaled by a yield-to-actual factor so the sum matches the plant's actual recovered liquids.
Theoretical yield begins with knowing what is in the gas. A gas chromatograph analyzes a producer's stream and reports the concentration of each hydrocarbon component - ethane, propane, isobutane, normal butane, and the heavier pentanes-plus. From those concentrations, the recoverable liquid content is expressed as gallons per thousand cubic feet, commonly written GPM, for each component. A rich gas might carry several gallons of recoverable liquids per thousand cubic feet across all components; a lean gas far fewer. GPM is essentially a statement of how much liquid, in principle, is hiding in each unit of that gas.
Multiplying the per-component GPM by the metered gas volume gives the theoretical number of gallons, and therefore barrels, of each liquid that the producer's gas could yield if every recoverable molecule were captured. Summed across components and across the accounting period, this produces a theoretical liquids figure for each producer. The two inputs are simple to name but exacting to get right: an accurate composition from the gas analyzer and an accurate volume from the meter. A wrong GPM or a wrong volume distorts one producer's theoretical yield and, because allocation is a shared pie, shifts the split for everyone else too.
No plant recovers every molecule its inlet gas theoretically contained. Real recovery depends on the plant's process design and how it is being run - a cryogenic plant recovers a far higher fraction of ethane than a refrigeration plant, and any plant may deliberately reject ethane to the residue stream when its liquid value does not justify recovery. Beyond design choices, ordinary operating conditions, ambient temperature, equipment efficiency, and the day-to-day tuning of the plant all mean the actual recovered barrels fall short of, and vary against, the theoretical total. Theoretical yield is a ceiling and a basis for sharing, not a promise of what comes out.
The gap between theoretical and actual is precisely why the theoretical figures cannot be paid out as-is. If the plant credited every producer with their full theoretical yield, the sum of the credits would exceed the liquids that actually exist, and the plant would be allocating barrels it never made. The purpose of theoretical yield is not to state each producer's exact recovery but to establish the proportion in which the real, smaller pool of recovered liquids should be divided. A producer with rich gas earns a larger theoretical yield and therefore a larger share of the actual barrels, but the actual barrels - not the theoretical ones - are what get allocated and paid.
The bridge from theoretical to real is the yield-to-actual factor: the ratio of the plant's total actual recovered liquids to the total theoretical yield summed across all producers. Each producer's theoretical figure is multiplied by this single factor to give their allocated actual barrels, so the allocated barrels add up exactly to what the plant recovered and measured leaving as liquid product. This method preserves the relative shares that composition and volume determined while forcing the total to reconcile with reality. It is fair because it divides shortfall proportionally: if the plant recovered ninety percent of the theoretical total, every producer receives ninety percent of their theoretical share.
Every input to this calculation traces back to measurement. The composition inputs come from gas chromatographs sampling each producer's stream; the volume inputs come from the inlet meters; and the actual recovered total comes from metering the liquids as they leave the plant. Errors or gaps in any of these ripple through the whole allocation. A cloud SCADA platform such as Merobix links the gas chromatograph and inlet metering into one timestamped record so the GPM and volume feeding each producer's theoretical yield are captured live and reconciled against the measured liquids recovery. That continuous, connected measurement is what lets an allocation be recomputed and defended, and it lets a producer see whether the composition and volume behind its theoretical yield match what its own field data shows.
GPM stands for gallons per thousand cubic feet - the recoverable liquid content of a gas stream, broken out by component such as ethane, propane, and butanes. It comes from a gas chromatograph analysis of the composition. Multiplying a component's GPM by the metered gas volume gives the theoretical gallons of that liquid the gas could yield, which is the starting point for allocating a producer's share of recovered barrels.
Because no plant captures every recoverable molecule. Recovery depends on the plant's process design - a cryogenic plant recovers far more ethane than a refrigeration plant - and on operating choices like deliberately rejecting ethane when its liquid value is low, plus ambient conditions and equipment efficiency. Theoretical yield is a ceiling used to set the proportions for sharing; the actual, smaller pool of recovered barrels is what gets allocated and paid.
It is the ratio of the plant's total actual recovered liquids to the sum of all producers' theoretical yields. Each producer's theoretical figure is multiplied by this factor to give their allocated actual barrels, so the allocations add up exactly to what the plant recovered. This divides any shortfall proportionally - if the plant recovered ninety percent of the theoretical total, every producer receives ninety percent of their theoretical share.
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