FIFO vs LIFO vs WACOG: How Natural Gas Storage Valuation Works
Natural gas storage is a straightforward concept: buy gas when demand is low or prices are favorable, inject it underground, and withdraw it later when you need it or can sell it at a profit. But the accounting behind storage is where things get interesting — and where mistakes can quietly distort financial statements.
The central question is deceptively simple: when you withdraw gas from storage that was injected at different times and different prices, what is the cost of the gas you just pulled out?
Why Storage Valuation Matters: The Matching Principle
Before getting into the methods, it is worth understanding why this matters at all. The answer lies in one of the foundational concepts in accounting: the matching principle.
The matching principle requires that you recognize as an expense only the cost of goods that have actually been sold in the current period. Gas sitting in storage has not been sold — it must be carried as inventory on the balance sheet, classified as a deferred expense.
Consider a simple example: you buy 10 units of gas at $3.00 each ($30 total investment), but you only sell 2 units this month at $10.00 each ($20 revenue). Under the matching principle:
- Cost of goods sold = 2 units x $3.00 = $6.00
- Gross profit = $20.00 - $6.00 = $14.00
- The remaining 8 units ($24.00) sit as inventory until sold
Without proper storage valuation, a company would show a massive loss when it buys and injects gas, then a massive artificial gain when it withdraws and sells — making financial statements volatile and misleading. The valuation method you choose determines how cost flows from the balance sheet to the income statement.
Three Methods, Three Different Numbers
Natural gas storage facilities accumulate inventory in layers. Each month’s injection may come at a different purchase price, transport cost, and fuel loss — resulting in a different per-unit landed cost for each layer.
Here is a realistic storage inventory with four injection layers:
| Injection Month | Volume (MMBTU) | Landed Rate ($/MMBTU) | Asset Value |
|---|---|---|---|
| July | 55,785 | $3.05 | $170,172 |
| August | 32,585 | $3.34 | $108,697 |
| September | 65,800 | $3.26 | $214,344 |
| October | 64,340 | $3.38 | $217,748 |
| Total | 218,510 | $710,961 |
Now suppose you need to withdraw 150,000 MMBTU. The three valuation methods will produce different costs of goods sold, different remaining inventory values, and different reported margins.
FIFO: First In, First Out
Under FIFO, the oldest gas is withdrawn first. The analogy is a grocery store shelf: the stocker pushes older bread to the front and places fresh bread in the back, ensuring the oldest product sells first.
For a 150,000 MMBTU withdrawal under FIFO:
- All 55,785 MMBTU from July at $3.05 = $170,172
- All 32,585 MMBTU from August at $3.34 = $108,697
- 61,630 MMBTU from September at $3.26 = $200,914
Total withdrawal cost: approximately $479,783 (average ~$3.20/MMBTU)
The remaining inventory consists of the most recently injected gas — the tail end of September and all of October — which in this case reflects higher costs. FIFO tends to produce lower cost of goods sold when prices are rising, which means higher reported profit.
LIFO: Last In, First Out
Under LIFO, the most recently injected gas is withdrawn first. The analogy is a warehouse with stacked drums: you take from the front (most recent) because the product does not spoil and there is no urgency to move older inventory.
For a 150,000 MMBTU withdrawal under LIFO:
- All 64,340 MMBTU from October at $3.38 = $217,748
- All 65,800 MMBTU from September at $3.26 = $214,344
- 19,860 MMBTU from August at $3.34 = $66,332
Total withdrawal cost: approximately $498,424 (average ~$3.32/MMBTU)
The remaining inventory consists of the oldest, lowest-cost gas — all of July and the balance of August. LIFO produces higher cost of goods sold when prices are rising, which means lower reported profit but also lower tax liability.
WACOG: Weighted Average Cost of Gas
Under WACOG, all injected gas is treated as co-mingled — there are no separate layers. Every withdrawal is valued at the blended average rate across the entire inventory.
WACOG rate = Total Asset Value / Total Volume
$710,961 / 218,510 = $3.254/MMBTU
For a 150,000 MMBTU withdrawal:
Total withdrawal cost: 150,000 x $3.254 = $488,100
WACOG is the most widely used method in the natural gas industry today because it is simpler to administer. There are no layers to track, no ordering logic to maintain — just a running average that updates with each injection.
When Each Method Is Advantageous
The choice of valuation method has real financial consequences:
FIFO works well when a company wants to report higher margins on its income statement. Because older (typically cheaper) gas is expensed first, cost of goods sold is lower when prices are trending up. The remaining inventory on the balance sheet reflects current market costs more closely.
LIFO is favored when a company wants to minimize taxable income. By expensing the most recent (and typically most expensive) gas first, LIFO increases cost of goods sold and reduces reported profit. This is a legitimate tax strategy, though the IRS requires that once a company selects LIFO, it must also use LIFO for financial reporting purposes (the LIFO conformity rule).
WACOG appeals to companies that prioritize simplicity and consistency. It smooths out the volatility that FIFO and LIFO can introduce when injection costs vary significantly across months. For regulated utilities subject to jurisdictional audits, WACOG’s transparency is an advantage.
Once a valuation method is selected, changing it requires IRS approval. This is not a decision that can be revisited casually.
Storage as a Balance Sheet Asset
Gas in storage is a tangible asset with measurable value. The ETRM (Energy Trading and Risk Management) system must track both the quantity (MMBTU) and the value (cost per MMBTU times volume) at every stage:
- Purchase price at the wellhead or trading hub
- Transport cost to move gas to the storage facility, including fuel retained by the pipeline
- Injection fees charged by the storage operator, plus injection fuel
- In-place charges (some facilities charge a per-MMBTU daily fee on the balance sitting in storage)
Each of these costs increases the per-unit landed cost. In the example above, gas purchased at $3.00/MMBTU might carry a landed injection cost of $3.38/MMBTU after accounting for transport ($0.15/MMBTU), fuel losses, and injection fees ($0.20/MMBTU). When that gas is withdrawn, additional costs apply: withdrawal fees, withdrawal fuel, and transport from storage to market. A unit that entered storage at $3.38 might carry an all-in delivered cost above $4.13 by the time it reaches the sales point.
The margin calculation is straightforward but unforgiving: the sales price must exceed the total all-in cost, or the trade loses money.
Storage vs. Imbalances: Both Are Inventory
A common mistake in gas accounting is treating storage inventory rigorously while ignoring imbalances. An imbalance occurs when the volume of gas a shipper puts into a pipeline does not match the volume delivered out — the physical system simply cannot achieve exact precision every day.
The critical distinction is intent: storage is deliberate and planned; imbalances are accidental and discovered after the fact. But both represent inventory with measurable financial value, and both require the same valuation treatment.
| Storage | Imbalance | |
|---|---|---|
| Intentional? | Yes | No |
| Created by | Physical injection | Variance between scheduled and actual flows |
| Valuation required | Yes — FIFO, LIFO, or WACOG | Yes — same methods apply |
| Financial impact | Deferred expense on balance sheet | Deferred expense on balance sheet |
A $10,000 imbalance sitting on a pipeline has the same financial statement impact as $10,000 of gas sitting in storage. Systems that fail to value imbalances produce inaccurate cost of goods sold and misleading inventory balances.
Why This Matters for CPAs and Financial Professionals
For accountants and auditors working in the energy industry, storage valuation is not an abstract exercise. It directly affects:
- Cost of goods sold on the income statement
- Inventory balances on the balance sheet
- Tax liability (FIFO vs. LIFO can produce meaningfully different taxable income)
- Regulatory compliance for utilities subject to state commission oversight
- Audit defensibility — regulators and auditors want to see consistent methodology and accurate landed-cost tracking
Understanding the mechanics of storage — how gas accumulates cost as it moves through the system, how valuation methods produce different financial outcomes, and why imbalances deserve the same rigor as storage — is a foundational competency for any financial professional working in natural gas.
The numbers are real, the methods are well-established, and the consequences of getting it wrong show up on every financial statement the company produces.