An investor buys an oil ETF because crude prices are rising. A month later, crude is up 5 percent. The ETF is flat — or negative. The investor sees theft. The reality is contango: a structural feature of the futures market in which the price of a commodity for future delivery exceeds the current spot price, imposing a cost on any investor who must repeatedly roll expiring contracts into more expensive ones. Understanding the shape of the futures curve — and the roll yield it generates — is the single most important determinant of whether a commodity investment makes or loses money, and it is the variable that the overwhelming majority of retail commodity investors do not know exists.
The Futures Curve: A Term Structure of Prices
A commodity does not have one price. It has a series of prices stretching into the future — one for each delivery month. West Texas Intermediate crude oil, for example, trades simultaneously for delivery in May, June, July, August, and every subsequent month through multi-year forward contracts. The collection of these prices, plotted chronologically, forms the futures curve.
When the curve slopes upward — each successive month is more expensive than the one before — the market is in contango. When the curve slopes downward — each successive month is cheaper — the market is in backwardation. The shape of the curve reflects the market's expectations about future supply and demand, the cost of storing the physical commodity, and the risk premium that speculators demand for bearing the uncertainty of future prices.
Contango: The Silent Tax on Passive Commodity Investors
A commodity ETF that tracks futures contracts cannot hold the underlying physical commodity indefinitely. Oil degrades. Natural gas requires cryogenic storage. Even gold ETFs that hold physical metal incur insurance and vault costs. Most commodity ETFs track futures contracts, and futures contracts expire. When the front-month contract approaches expiration, the fund must sell it and buy the next month's contract — a process called "rolling."
In contango, the next month's contract is more expensive than the expiring contract. The fund sells the cheap expiring contract and buys the expensive next-month contract. The difference is a loss — the roll cost — that compounds every month. Over a year, the cumulative roll cost can consume 5 to 15 percent of the fund's value, even if the spot price of the commodity has not changed.
The United States Oil Fund (ticker USO) is the most infamous example. Between 2009 and 2020, crude oil prices were broadly flat in spot terms. USO lost approximately 90 percent of its value. The destruction was not caused by falling oil prices. It was caused by eleven years of monthly roll costs in a persistently contango market. The spot price of oil and the return of the oil ETF diverged so dramatically that USO became a case study in the gap between what retail investors think they are buying and what they actually own.
Backwardation: When the Curve Pays You to Hold
Backwardation is the inverse: the front-month contract is more expensive than the next month. When the fund rolls, it sells the expensive front-month and buys the cheaper next-month — generating a positive roll yield. The fund earns money from the rolling process itself, independent of whether the spot price of the commodity rises or falls.
Backwardation typically occurs when immediate physical demand exceeds available supply — when refiners need crude oil now, when utilities need natural gas today, when industrial users need copper for current production. The premium on the front month reflects the urgency of current demand relative to the market's expectation of future supply.
Commodities that spend the majority of their time in backwardation — such as crude oil during supply disruptions, or agricultural commodities during drought — reward passive holders with positive roll yield. Commodities that spend the majority of their time in contango — such as natural gas and VIX futures — systematically destroy the value of passive long positions.
The VIX Futures: The Most Extreme Contango in Financial Markets
VIX futures exist in persistent, steep contango under normal market conditions. The current VIX spot might trade at 14 while the two-month VIX future trades at 18. This contango reflects the market's expectation that volatility will revert toward its long-term average — an expectation that is statistically correct approximately 80 percent of the time.
ETFs and exchange-traded notes that track VIX futures — such as the iPath Series B S&P 500 VIX Short-Term Futures ETN (ticker VXX) — roll from cheap near-term contracts into expensive further-dated contracts every day. The result is a systematic value destruction that has caused every long-VIX product to lose 90 percent or more of its value over any multi-year holding period. These products are designed for intraday hedging, not for long-term holding. The investor who buys VXX as a "portfolio hedge" and holds it for six months will almost certainly lose money — even if a volatility spike occurs during the holding period — because the roll cost exceeds the spike benefit in the majority of scenarios.
How to Evaluate a Commodity Investment
Before committing capital to any commodity ETF or futures-linked product, the investor must answer three questions. First, is the futures curve currently in contango or backwardation? The curve shape is publicly available from the exchange (CME Group publishes futures prices for every commodity and expiration on its website) and from data providers like Quandl and Bloomberg.
Second, what is the historical roll yield for this commodity? Commodities like crude oil alternate between contango and backwardation depending on supply conditions. Commodities like natural gas and VIX futures are in contango the vast majority of the time. The historical roll yield determines the structural cost of holding the position.
Third, does the ETF use a front-month rolling strategy (which maximizes contango cost but tracks spot price most closely) or an optimized strategy that selects contracts based on curve shape to minimize roll cost? The United States 12 Month Oil Fund (ticker USL) distributes its holdings across twelve monthly contracts, reducing the concentration of roll cost in any single month. The Invesco Optimum Yield Diversified Commodity Strategy ETF (ticker PDBC) uses an algorithmic approach to select the contracts with the most favorable roll economics.
The futures curve is not a technicality. It is the primary determinant of commodity investment returns. The investor who buys a commodity ETF without examining the curve shape is entering a trade whose most important variable is invisible — and in contango markets, the invisibility costs money every month, compounding silently until the portfolio statement reveals the damage.