Broad commodity ETFs split on oil weight and which contract they hold

The funds sold as a broad basket of commodities did not have the same year. From the last close of 2025 through September 30, shares of CGSG, the iShares trust that tracks the S&P GSCI, rose 54.2%. Shares of ABCI, Aberdeen's fund that tracks the Bloomberg Commodity Index, rose 32.5%.

Brent crude rose 61% over that stretch, from $60.85 to $98.03. Gold futures fell 3.6%.

The two funds track different indexes, so they are allowed to hold different amounts of oil. Other funds in the same index family hold a different contract, and their returns split too.

Two indexes were built to disagree

The S&P GSCI is a world production-weighted index. S&P Dow Jones Indices set its 2026 energy target at 51.8%, in force since the January roll. Brent's target is 18.2% and WTI's is 17.8%, so 36% of the index is two crude contracts.

Natural gas is 3.6% of that index, a small part of the energy weight. Gold's target is 7.2%.

The Bloomberg index is built to stop that concentration. CME Group, which lists futures on it, describes the weights as one-third world production and two-thirds trading liquidity, then capped so no commodity exceeds 15% and no sector exceeds 33%. Under that cap, an energy weight of 51.8% cannot happen.

Bloomberg's announcement on October 30, 2025 set the January 2026 energy target at 29.4%. Brent's target is 8.36% and WTI's is 6.64%. Natural gas is 7.2%, a larger slice than gas has in the GSCI.

Those are January targets. S&P says the weight on any day moves with prices. When oil rises faster than the rest of the basket, its share of a production-weighted index rises with it until the next reset.

The same announcement raised gold's 2026 target to 14.9%, from 14.3%. The GSCI's gold target is 7.2%. ABCI's index has the larger gold target, and gold's 3.6% decline would have held that fund back.

Nicholas Godec of S&P Dow Jones Indices set out the other side of that energy weight in a July study. In past periods of high inflation, when consumer prices were rising 5.8% a year, the GSCI's trailing yearly gain averaged 33.4%, against 21.1% for the Bloomberg index. In low-inflation periods the same construction averaged a 9.7% loss, and the Bloomberg index averaged a 4.4% loss.

Those are historical averages, not a forecast. In both regimes, the index with more energy moved further.

Which contract they hold is the other split

Open the holdings and the largest line is often cash. On October 1, 40.7% of ABCI's reported assets sat in a government money-market fund, and CGSG's reported holdings are Treasury bills. Futures are a promise that has to be backed, so the cash sits under the contracts, and the commodity exposure is in the contracts themselves.

The return has three parts. The contract's price changes. The fund replaces the contract before it expires, and the gap between the one it sells and the one it buys can add or subtract.

The collateral earns interest. The three-month Treasury bill yielded 4.17% on October 1, and both total-return indexes add a Treasury-bill return to the futures.

If the later contract costs more than the expiring one, a state called contango, the fund sells cheaper and buys dearer. That cost comes out even when the spot price has not fallen. A cheaper later contract works the other way.

Aberdeen runs the comparison inside one index family. Its longer-dated fund, ABCD, tracks the Bloomberg Commodity Index 3 Month Forward. Aberdeen's prospectus dated May 1, 2026 says the Bloomberg index tracks futures with a maturity of one to three months, and that ABCD's forward index holds futures with a maturity of four to six months.

ABCD charges 0.30%, against 0.26% for ABCI, and holds $0.44 billion. Its shares rose 24.3%, 8.2 percentage points behind ABCI. A fee gap of 0.04 percentage points cannot account for a return gap of that size.

iShares' dynamic-roll version of the GSCI, BCOMT, holds $1.39 billion and charges 0.49%, against 0.75% for the plain trust. It rose 48.1%, 6.1 percentage points behind CGSG.

Our read is that the larger oil allowance caught more of the oil rise, and that the choice of contract moved returns even when the basket did not change.

Invesco's APDBC is the largest fund in the group, at $7.70 billion. It is actively managed and uses a rule to choose the contract. Invesco's prospectus dated February 27, 2026 lists a net expense ratio of 0.59%, after a waiver through August 31, 2027.

State Street launched ACERY on September 4, 2024 to track an enhanced-roll Bloomberg index. The issuer says it favors commodities on a downward-sloping curve, where a later contract costs less. It holds $1.14 billion and charges 0.28%.

Share-price changes in the table run from the last close of 2025 to September 30. None of these funds paid a distribution in that window, so the figure is also what a holder earned. Assets are the latest figures on file, from September 29 to October 2.

iShares says the trust behind CGSG is not registered under the Investment Company Act of 1940, and describes an investment in it as speculative.

The fund that held more oil has more to give back

The Energy Information Administration's September 9 outlook had Brent averaging $91 a barrel this year and $74 in 2027. Brent closed September 30 at $98.03, above the agency's average for 2026. The agency assumes some constraints on Middle East oil exports will persist through the end of the year, and that production in the region stays below pre-conflict averages until the second quarter of 2027.

The 2027 figure is a path down, and CGSG, the fund with more oil, is the one that would feel it.

The International Energy Agency's September report put observed inventory draws since February at 507 million barrels. In August, more than 10 million barrels a day of Gulf output remained shut in. The agency forecast 2026 oil demand 2.5 million barrels a day below 2025.

CME Group wrote on March 17 that investor focus had shifted to oil amid the Mideast conflict. On July 27 it wrote that crude prices had retreated from peaks set between March and May, and said the conflict began on February 28.

A broad commodity fund is a chosen amount of oil, a chosen month on the curve, and a Treasury bill, and the name does not tell you which.