The Samuelson Effect in Futures Volatility
A futures contract with only a week left to expiry tends to jump around a lot more than the same commodity's contract expiring a year from now — a well-documented pattern named after economist Paul Samuelson.
Prerequisites: Commodity Futures Basics, Contango and Backwardation
Watch a commodity's front-month futures contract into its final trading week and, more often than not, it whips around noticeably more than the contract expiring a year out. This is not random noise — it is a persistent, documented regularity called the Samuelson effect: implied and realized volatility in futures typically rises as a contract approaches expiry, and near-dated contracts are usually more volatile than far-dated ones on the same underlying commodity.
The Samuelson effect says futures volatility tends to increase as expiry approaches, because near-term supply-and-demand news (a weather event, a refinery outage, an unexpected inventory report) has nowhere to be absorbed except into a price that is about to be locked in, while the same news barely moves a contract a year out, since there is plenty of time for supply and demand to adjust before that far-off delivery date arrives.
Why time-to-expiry itself changes volatility
A distant futures contract prices in an expectation averaged over everything that could plausibly happen in the underlying market between now and that far-off delivery date — droughts might hit, but so might bumper harvests; one week's cold snap barely dents a forecast a year ahead, because there is a full year for conditions to normalize. A contract expiring next week has no such luxury: today's weather, today's inventory report, and today's shipping bottleneck are close to being the entire determinant of the delivery-month price, because there is almost no time left for anything to average out or reverse. The same piece of news that nudges the far contract barely at all can move the near contract sharply, simply because the near contract has run out of time to "wait and see."
Worked example
Suppose the 12-month natural gas futures contract has an annualized implied volatility of 25%, while the front-month contract, three weeks from expiry, shows implied volatility of 55% — more than double, despite both contracts referencing the same underlying commodity. A cold snap that shaves a few percent off expected national gas inventories moves the front contract sharply because delivery is imminent and there is no time for supply to respond; the same cold snap barely moves the 12-month contract, since producers, importers, and consumers all have a full year to adjust behavior before that far-off month actually arrives.
What this means in practice
Options and volatility traders build the Samuelson effect directly into how they price and hedge commodity options: an option's implied volatility is not just a function of the underlying commodity's general "riskiness" but also of how much time is left until the futures contract itself, not just the option, expires — which is why commodity vol surfaces are typically built with term structure as a first-class dimension, not an afterthought.
The Samuelson effect is a tendency, not an ironclad rule, and it can be swamped by structural forces like storage constraints or persistent event risk further out the curve (a hurricane season priced months in advance, for instance). Do not assume every commodity's near-dated contract is automatically more volatile than its far-dated one without checking the specific term structure — some commodities, especially those prone to major weather events far in advance, can show a much flatter or even inverted pattern.
Related concepts
Practice in interviews
Further reading
- Samuelson, 'Proof That Properly Anticipated Prices Fluctuate Randomly' (1965)