Amaranth Advisors Natural Gas Collapse

In September 2006, Amaranth Advisors, a Greenwich-based hedge fund with $9 billion in assets under management, went from a respected mid-tier energy-focused fund to near-total insolvency in two weeks. The culprit was a massive, concentrated bet on the spread between natural gas prices in different months—a bet that was essentially a huge leveraged wager that autumn would be unusually cold and natural gas expensive. When prices collapsed instead, the trader responsible—a single individual with nearly unlimited discretion—turned Amaranth into a cautionary tale about concentrated risk, counterparty risk, and the fragility of leverage when liquidity evaporates.

The natural gas spreads trade

Amaranth’s core business was energy trading, particularly natural gas futures. The fund had hired Brian Hunter in 2003, a young trader with a strong track record. Hunter built Amaranth’s energy desk into a profitable operation, and over several years the fund rewarded him with increasing leverage and autonomy.

By 2006, Hunter had begun focusing on a specific trade: the calendar spread in natural gas futures. A calendar spread is a position where you go long (buy) a futures contract expiring in one month and go short (sell) a contract expiring in another month, betting that the difference in price between those two months will move in your favour.

Natural gas prices are volatile and seasonal: spring and fall are mild, summer and winter are extreme. A trader might bet that November natural gas will trade at a much higher premium to September natural gas during the autumn, because heating demand will spike. If you buy November and sell September, you profit if November rises relative to September—if the spread widens.

Hunter built a position with enormous notional exposure: he was long roughly $1 billion notional in calendar spreads across multiple months, all concentrated in the belief that autumn would be cold and demand would be strong. He was using leverage; Amaranth was not posting $1 billion in cash, but rather margin, borrowing most of the capital from their broker-dealers.

The bet becomes a trap

For the first part of 2006, the trade was profitable. Natural gas prices were volatile, and spreads moved in the expected directions. Hunter’s returns contributed significantly to Amaranth’s overall performance. The fund’s management, impressed by his results and desperate for alpha in a flat market, gave him even more capital and leverage to work with. By September, his position had grown to notional sizes that exceeded the entire fund’s capital—a classic sign of extreme leverage.

The fatal flaw: his position was essentially a bet that autumn 2006 would be cold. If it was mild, demand would be weak, heating loads would not materialize, and natural gas prices would collapse. Moreover, the calendar spreads themselves would compress—the seasonal premium would disappear.

In early September, weather forecasts began suggesting a mild autumn. At first, Hunter held firm, believing the forecast was wrong and that demand would still be strong. But by mid-September, it became clear: autumn 2006 would indeed be unusually mild, and natural gas prices were tanking.

As prices fell, Hunter’s position moved from profitable to deeply underwater. More critically, the leverage trapped him: to close a $1 billion notional position during a market decline, you must sell into weakness. Every attempt to exit the position pushed prices lower, which increased his losses, which forced larger exits.

The liquidity crisis and the margin calls

The real catastrophe struck when Amaranth’s broker-dealers lost confidence. When a counterparty (the broker providing leverage) believes the borrower might not be able to repay, they can issue a margin call: a demand for immediate cash. If the cash is not posted, the broker has the right to forcibly liquidate the position.

In the week of September 18, Amaranth’s brokers—JPMorgan, Goldman Sachs, and others—began issuing margin calls. Amaranth posted margin, but only briefly. By September 20, the size and speed of the selling had exhausted Amaranth’s reserves, and the brokers began liquidating the natural gas positions themselves, without waiting for Amaranth’s consent.

This is where liquidity risk turned theoretical into operational catastrophe. The natural gas futures market is deep and liquid—in ordinary times. But when a single large trader needs to exit a $1 billion position all at once into a market that is already weak, there are not enough buyers at any reasonable price. The forced liquidation pushed prices down further, which both amplified the losses and ate away the value of the remaining positions.

Within 14 days, Amaranth lost approximately $6 billion. The fund went from $9 billion in assets to roughly $2 billion, and even that was only because the remaining positions were liquidated urgently and at severe discounts.

Governance failure and the aftermath

In retrospect, Amaranth’s collapse was not a market surprise or an unforeseeable event. It was a governance catastrophe. Hunter had been given massive leverage, authority to build enormous single-position bets, and virtually no oversight. Risk controls that should have flagged a $1 billion notional position in a single trader’s account either did not exist or were ignored. The fund’s risk managers did not understand the exposures in calendar spreads, or did not have the standing to push back against Hunter’s increasingly aggressive positioning.

The broader lessons were grim:

First, concentrated risk in a single trade is not diversified risk. Amaranth called itself a hedge fund, suggesting it was hedged, but it was a highly concentrated bet on natural gas spreads. When that bet went wrong, there was no diversification to cushion the blow.

Second, leverage is a two-edged sword. It amplified gains when the trade was winning, attracting capital and complacency. When the trade reversed, the same leverage forced instant liquidation, preventing the fund from ever having the option to hold and recover.

Third, counterparty risk is real during stress. The brokers were justified in issuing margin calls; Amaranth was indeed at risk of insolvency. But the forced liquidation was brutal. A trader or fund facing this pressure will always lose the most to the house during liquidation.

Amaranth was sold for parts. JPMorgan Chase agreed to take over the remaining positions at a discount, partly out of self-interest (to stop the rapid-fire liquidations that were destabilizing the market) and partly because the positions were still valuable if held for recovery.

The human cost and the policy response

Brian Hunter was heavily criticized by regulators and in the press. The Commodity Futures Trading Commission (CFTC) later fined Amaranth and Hunter for violations. Hunter’s reputation was destroyed, though he later rebuilt some credibility trading at other firms.

The broader impact was policy change. Regulators began scrutinizing hedge fund leverage more closely and required more transparent counterparty risk disclosures. The event also highlighted the fragility of energy markets and sparked debates about position limits and leverage caps for commodity traders.

For later traders and funds, Amaranth became the historical reference: a $6 billion reminder that a single trader with conviction, leverage, and no real oversight can destroy a billion-dollar institution in a matter of days. The trade was not inherently wrong—the thesis that natural gas would be expensive in autumn 2006 was reasonable. But the size, the leverage, and the concentration guaranteed that when the thesis failed, it would fail catastrophically.

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