You have read that commodities protect you from inflation and cushion a bad year in stocks. That claim is defensible. What usually goes missing is the rest of it: what commodities have actually returned, why a fund tracking oil can lag the oil price by a wide margin, and what a sensible position size depends on.
The Honest Case Is Not About Returns
A share of stock has a company behind it, earning money and putting some of it back to work. A bond pays coupons. A barrel of oil does neither. It sits in a tank and costs money to stay there. Nothing compounds, because there is no cash flow to compound. Your whole result rests on what someone else pays later.
That shapes what you should expect. In a 2006 study, Claude Erb and Campbell Harvey found that the average individual commodity futures contract had earned an excess return of roughly zero over its history. Gary Gorton and Geert Rouwenhorst published the same year and found something that sounds contradictory: an equally weighted, rebalanced basket of commodity futures matched stocks for return from July 1959 to March 2004. Both are right. The basket beat its own parts because rebalancing it, trimming what had run and adding to what had fallen, generated a return no single contract had.
Gorton and Rouwenhorst also found commodity futures moved with inflation, including the part nobody saw coming, while stocks and bonds moved against it. That is the real case. You are buying a different reaction to inflation, not a growth engine.
The Price You See Is Not the Return You Get
Most commodities cannot be stored by a fund, so funds buy futures contracts instead. A futures contract is an agreement to take delivery of a set amount on a set date. The fund does not want the oil, so before the contract expires it sells that one and buys the next month's. That swap is the roll, and it repeats every month forever.
The price quoted on the news is the spot price, for delivery now. The fund never owns that. It owns a contract for a future month, and the gap between the two is where a fund's return separates from the headline. The article on buying commodities names this problem; here is the arithmetic.
What the Roll Costs, in Numbers
Say the fund controls 100 barrels at $80, so $8,000 of exposure. Next month's contract trades at $80.80, one percent higher. When it rolls, that $8,000 now buys about 99 barrels. Spot did not move. You own less oil than you did.
Run that twelve times with the curve holding its shape and you finish the year controlling roughly 89 barrels. About eleven percent is gone, and no fee took it. Futures priced above spot like this are in contango. When the next month is cheaper than this one, called backwardation, the roll runs the other way and each swap buys more barrels than you had.
Nobody pockets the roll. It is what the shape of the futures curve costs. A contango curve usually means storage is expensive or supply is piling up, so you are paying the market to avoid renting a tank yourself.
The Treasury Bills Sitting Behind the Contracts
Futures do not require the full value up front. A fund controlling $8,000 of oil might post a few hundred dollars as margin and park the rest in Treasury bills. That interest is not a rounding error. It is the third piece of the return, alongside the spot move and the roll.
This is why the same strategy looks so different across decades. If short-term rates sit near 5 percent, collateral alone adds about five points a year before any commodity does anything. If rates sit near zero, that piece vanishes and prices have to carry the whole load. Nothing about the commodities changed.
Index providers publish both versions. An excess return index counts spot and roll only. A total return index adds the collateral interest. A fund's documents say which one it follows.
Miners and Drillers Behave Like Stocks
The other route in is owning the companies that dig it up, and that changes your exposure more than most people expect.
A producer's costs are mostly fixed. A mine costs about the same to run whether copper sells high or low, so a modest price move swings profits hard in both directions. Producer shares often move further than the commodity does.
They are still stocks, though. In a broad market selloff they drop with everything else, which is the exact moment the diversification was supposed to help. Many producers also hedge their own output with futures, locking prices in months ahead, so a spike reaches shareholders in muted form. Their costs are commodity linked too, since diesel and steel get expensive in the same boom that lifts revenue.
What you get in return is real: earnings, often dividends, and a business that can grow. The company-level risks that come with it are covered in the piece on buying commodities.
The Paperwork Some Structures Create
Many broad commodity funds are organized as commodity pools and taxed as partnerships, not as ordinary funds. Two things follow, and neither is visible from the ticker.
You receive a Schedule K-1 instead of the 1099 a stock fund sends. It is a longer form, and it often lands later in the filing season than your other documents.
The futures inside are Section 1256 contracts. The IRS marks these to market at year end. Gains count as realized on the last business day of the year whether or not anything was sold, and they split 60 percent long-term and 40 percent short-term no matter how long you held the position. Since the pool is a partnership, that passes through to you. You can owe tax on a gain in a fund you never traded.
Not every commodity fund works this way. Some are built to send a 1099. Others are exchange traded notes, which are unsecured debt of a bank rather than a claim on real assets, so you carry that issuer's credit risk. Physically backed metal funds get their own treatment, which the article on gold covers.
Sizing Is a Question About Volatility
Broad commodity exposure swings harder than a stock index over many stretches, so a small dollar weight can still move your portfolio a lot. The useful question is how much of your portfolio's total movement the position explains, not what share of the money it holds.
Three things decide whether it earns its place.
Whether you will rebalance. The diversification benefit is not automatic. It appears when you sell some after a run and buy some after a slump. That is the mechanism that made the rebalanced basket in that 1959 to 2004 study beat its own parts.
Your holding period. Commodities have trailed for a decade at a stretch. A position you will give up on after three bad years is one you will sell near the bottom.
What is actually inside. The big benchmarks weight by how much the world produces or trades. The world moves far more oil and gas by value than coffee, so energy is the largest block in the major indexes. A broad commodity fund is usually more of an energy bet than its name lets on.
