1. Begin With the Simplest Idea: Gas Moves Through Pipelines, Not Wires
Electricity is generated and consumed within the same instant. Gas is not. A molecule produced at a Cooper Basin wellhead this morning might reach a Melbourne stovetop three days later, having travelled through several pipelines and possibly sat in storage along the way. That physical lag is the single fact that makes gas a different kind of market to electricity.
Because gas can be stored in the pipe itself, not just in dedicated storage facilities, a system does not need supply and demand to match to the terajoule at every instant the way the electricity grid does. It needs them to match closely enough, over a day, that pipeline pressure (linepack) stays within a safe operating band. That tolerance is what gives gas markets their own physical vocabulary: nominations, allocations, linepack, and a "gas day" that runs 06:00 to 06:00 rather than midnight to midnight, because operationally that is when a pipeline's daily cycle actually resets.
The consequence for a reader is this: a gas system can look calm in aggregate while running genuinely tight in one corner of it. A pipeline's own linepack, not a national supply-demand balance, is usually the first thing to show stress.
- TJ/day: flow
- Terajoules per day is the standard east coast unit for a pipeline's throughput or a facility's daily production or demand.
- Linepack
- The gas physically held in a pipeline at any moment; it rises and falls as receipts and deliveries drift apart through the day.
- Gas day
- 06:00 to 06:00 Australian Eastern Standard Time, the operational day every pipeline and facility reports against.
2. What Is Inside the System?
Production is concentrated in a handful of basins: the Cooper-Eromanga in South Australia and Queensland, the Surat-Bowen in Queensland, and Gippsland and Otway in Victoria and Bass Strait. Gas from these basins reaches consumers through a network of transmission pipelines radiating from two dominant hubs, Wallumbilla in Queensland and Moomba in South Australia, each a fan-out point where several pipelines meet.
Storage facilities such as Iona in Victoria hold gas produced in summer for withdrawal in winter, smoothing a demand curve that is sharply seasonal in the southern states. And since 2015, three LNG export trains at Curtis Island near Gladstone (QCLNG, GLNG and APLNG) draw enormous volumes of Surat and Bowen basin gas, chill it to a liquid, and load it onto ships bound for Asian buyers under long-term contracts.
AEMO's Gas Bulletin Board is not a trading venue. It is a daily public disclosure regime: every registered facility and pipeline reports what it produced, received, delivered or held. Flow Trace is built entirely from that disclosure, which is why it can show what moved but has to infer, rather than directly observe, which receipt fed which delivery whenever a pipeline serves several points at once.
3. Linepack Is a Buffer, and It Can Run Thin
A pipeline operator nominates expected receipts and deliveries each day, but real-world flows never match a forecast exactly. Linepack absorbs the difference: a pipeline running a small receipts surplus builds pack, one running a deficit draws it down. AEMO monitors each pipeline's linepack against its own safe operating range and publishes a linepack capacity adequacy flag when the margin gets tight.
A flag of "threatened" or "inadequate" does not mean gas has run out. It means the physical buffer that absorbs the ordinary daily mismatch between nominations and reality has shrunk to the point where a further shock, a cold snap, a compressor outage, an unplanned production drop, would leave the pipeline with less room to cope than usual. That is a forward-looking risk signal, not a shortage.
Some pipelines run tight on almost every assessed day rather than occasionally. Flow Trace calls that chronic rather than episodic, because treating a structural condition the same way as a one-off event buries the more useful finding: certain corridors, most persistently the pipelines feeding Curtis Island, operate with routinely thin headroom as a normal state of affairs, not as a crisis.
4. How Gas Actually Trades
Unlike the NEM, where nearly all electricity clears through one centrally dispatched pool, most east coast gas changes hands through bilateral, privately negotiated contracts between producers, retailers and large users, often running for years and rarely disclosed in detail. AEMO operates two smaller, genuinely public markets alongside that private layer: the Declared Wholesale Gas Market in Victoria, and Short Term Trading Markets at the Sydney, Adelaide and Brisbane hubs, where a portion of daily supply and demand is matched at a published, transparent price.
Wallumbilla and Moomba also host voluntary Gas Supply Hubs, order-book venues where shippers can trade standardised daily and monthly gas products. These give a genuine, if comparatively thin, price signal near the two points where most of the network's gas actually changes custody.
The Bulletin Board Is Not the Market
It is worth being precise about what Flow Trace can and cannot show. The Bulletin Board discloses physical flow, not price. It says how much gas moved where, not what it sold for. A reader wanting the price side of the story needs the STTM, DWGM and Gas Supply Hub data separately; Flow Trace's own commercial half, what the export link costs the domestic market in price terms, is explicitly not yet built, and the page says so rather than implying a view it cannot honestly support.
5. Why the LNG Link Changed the Market's Character
Before 2015, east coast gas was a largely self-contained domestic market: production, broadly, served domestic demand, and prices reflected the cost of developing new supply for local buyers. Curtis Island's three LNG trains changed that permanently. Once producers could sell gas into a global market at prices linked to Asian LNG benchmarks, a domestic buyer's opportunity cost stopped being "what the next domestic supplier would charge" and became "what that gas could earn if it were exported instead."
That is the structural contradiction Flow Trace exists to measure: a country exporting most of its gas from one coast while the domestic market at the other end of the same pipeline network pays a price increasingly anchored to a benchmark set thousands of kilometres away. LNG export now accounts for the large majority of all east coast gas demand; generation, industry and households divide what is left.
That domestic remainder is not evenly shared. Generation is a comparatively small share of total demand but a decisive one for electricity, because a gas-fired power station only runs when the wholesale electricity price it can earn clears the gas price it must pay for fuel. Gas therefore sets a floor under NEM prices in every region where it is the marginal generator, which makes the gas price a quiet input into the electricity price even for a reader who never looks at a gas chart.
6. The Central Commercial Question: Who Bears the Cost of the Link?
Joining a domestic market to a global one through an export terminal is not inherently good or bad; it is a structural fact with a distribution of winners and losers. Producers gain access to a much larger, typically higher-paying buyer pool. Domestic consumers, in principle, gain security of long-run investment in new supply that a purely domestic market might not have justified.
The open question is whether the domestic remainder pays a cost for that link worth measuring directly, rather than assuming it nets out. A regional pattern is part of the answer: storage in one state can sit near a record low while another sits comfortably above normal, a divergence a single national number would hide entirely, and Victoria's own domestic load is understated by facility-reported figures precisely because Melbourne is served through a transmission system rather than facilities that report demand directly. Measuring the system honestly means holding both the export story and these regional distortions in view at once, rather than collapsing either into an average.
7. What a Gas Market Analyst Wants to Know
An analyst begins with physical truth. Which pipelines are tight today, and is that new or chronic? What is storage doing relative to the same point in past seasons? Did every facility that should have reported today actually report? A single day's figures are only meaningful once their coverage and quality are established.
The second layer is structural position. Where does each state sit on supply versus demand, both by facilities that report directly and by what pipelines actually delivered into it? Which corridors carry the largest flows, and how much of that routing is a direct measurement versus an inference across several receipt and delivery points?
The third layer is the export relationship specifically. What share of total demand is LNG export taking this quarter versus the same quarter last year? Is the domestic remainder growing, shrinking, or holding steady in absolute terms even as the export share moves? Gas-fired generation demand is the most price-sensitive part of that remainder, so its trend says something about how the electricity market is leaning on gas as a marginal fuel.
The fourth layer is what remains genuinely unknown from public data alone: contract prices, hedging positions, and the commercial terms behind any single flow. Public disclosure under the Bulletin Board is a floor of observability, not a complete picture, and a careful reader treats the gap between the two as itself informative rather than papering over it with an assumption.
8. How to Read Flow Trace
Start with the system snapshot. Every figure there sits against the same week in every other year on record, because a level without history is not a finding; the LNG export tile leads because it is the number the rest of the page's thesis rests on.
Next, the flow chart ranks every location's net position, supply against demand, for the current gas day, with Curtis Island's export flow called out on its own scale so it does not flatten every domestic location beneath it. The "largest flows" table underneath carries the same figures as plain numbers, with an explicit flag wherever a route is an allocated inference rather than a direct measurement.
Utilisation and the constraint history answer a narrower, more operational question: which pipelines are running close to their rated capacity, and has that been a one-off day or a structural pattern across the whole window. Storage answers a seasonal one: is the system carrying more or less buffer into the months ahead than it usually would at this point in the year.
The export-and-domestic-remainder chart, generation by station, and the state balance table together are the demand side of the story: how much gas leaves as LNG, what the domestic remainder is actually used for, and how unevenly that remainder is spread across states. Read together, they are Flow Trace's attempt to hold the export story and its domestic cost in the same view, rather than letting either one stand in for the whole system.