Two Oil
Prices
In the week to 25 September, US crude fell 7.9% while Brent rose. The gap between the two benchmarks hit its widest since May. Headlines said "oil fell". For Indonesia it did not. This report explains why the benchmarks split, why Indonesia pays the Brent side, and how that flows through the budget, the current account, and the rupiah.
Executive Summary
Most oil headlines quote WTI, the US benchmark. Last week WTI settled at $92.41, down $7.89 or 7.9%, its first weekly fall in six. Brent, the international benchmark, settled at $104.32, up 0.4%. The gap between them went from about $3.60 to about $11.90 in five sessions.
The split has two causes, and both are American. Talks between Washington and Tehran at the UN raised hopes of a truce, and talk of a US ban on diesel exports threatened to strand US crude at home. Neither changed much for the barrel that has to cross the Middle East or the Pacific to reach a buyer.
Indonesia prices its own crude off Dated Brent, and it imports well over half the oil it uses. The relief in US crude last week did not reach Indonesia's oil bill. For the budget, the current account, and the rupiah, the number that matters is the one that held above $100.
The Week the Benchmarks Split
Crude started the week lower after President Trump said he was open to talking to Iran at the UN, which pushed US crude back below $100 on Monday. It snapped a five-day losing streak on Wednesday when Iran said it would not surrender. On Friday both benchmarks fell about 2% as truce hopes built and diesel ban talk spread, even as Houthi attacks on Saudi Arabia kept supply risk alive.
| Benchmark | Fri 18 Sep | Fri 25 Sep | Change |
|---|---|---|---|
| WTI (US) | $100.30 | $92.41 | −$7.89 (−7.9%) |
| Brent (international) | $103.87 | $104.32 | +$0.45 (+0.4%) |
| Brent − WTI | $3.57 | $11.91 | +$8.34 |
Intraday on Thursday, WTI traded as much as $12.02 under Brent, its largest discount since 6 May. The cross-asset tape that week makes the same point from the other direction. Global risk was fine: Bitcoin closed the week up about 4%. Indonesian assets, which trade on the Brent side of the split, were not.
Bar length shows the size of each weekly move; green marks a move that helps an Indonesian holder (cheaper oil, higher Bitcoin), gold one that hurts. The JCI fell 3.09% to 6,241.89 on more than Rp3 trillion of net foreign selling, and the rupiah weakened from 17,758 to 17,902.
Section 03Why WTI Fell and Brent Did Not
Diesel politics hit US crude directly
President Trump floated banning US diesel exports to bring down record pump prices, and a 90-day ban was reported to be under discussion despite a White House denial. The US supplies roughly a fifth of global diesel exports. If refiners cannot sell diesel abroad, they run less crude. Analysts estimated runs could fall by as much as 12%, with key storage hubs filling within a month. That is bearish for WTI specifically, because it strands barrels inside the US.
Freight blocks the arbitrage
In a normal market, a wide discount would send cheap US crude abroad until the gap closed. That is not happening. Moving a very large crude carrier from the US Gulf Coast to Asia now costs around $50 million per voyage, about three times pre-war levels. The discount US crude needs to compete with a European barrel has roughly doubled, from about $4 to about $8. US crude exports rose just 45,000 barrels a day from July to August and were on track to fall for a third month in September.
Truce hopes are priced where the supply is safe
Talks at the UN raised hopes of a path to ending the war and reopening the Strait of Hormuz. Iran said it would restart talks toward a final deal if the US implemented the conditions of the earlier memorandum of understanding. Those hopes pushed down both benchmarks on Friday. But Brent still carries the Middle East supply and shipping premium, and Houthi attacks on Saudi Arabia kept that premium in place.
The spread is not a pricing error waiting to be arbitraged away. It is a freight and policy wall. As long as tankers cost three times their pre-war rate and Washington is weighing export limits, cheap US crude stays in the US. Asian buyers pay Brent-linked prices.
The Spread in 2026
This is the second time this year the spread has blown out. The first was in March, when the war first closed Hormuz. On 18 March the gap reached its widest since January 2014, before the US lifted its crude export ban. The EIA reported that the spread averaged about $11–12 in March and peaked near $25 on 31 March.
| Date | Brent − WTI | Driver |
|---|---|---|
| 18 Mar | ~$12 | Widest since Jan 2014; Hormuz disrupted |
| 31 Mar | ~$25 peak | Shipping capacity shut in; SPR releases cap WTI |
| March avg | ~$11–12 | Highest monthly average in 5+ years (EIA) |
| 18 Sep | $3.57 | WTI above $100 during Saudi pipeline outage |
| 24 Sep | $12.02 intraday | Widest since 6 May; diesel ban talk |
| 25 Sep | $11.91 | Truce hopes hit WTI harder than Brent |
The March episode had the same structure as this one. Brent was exposed to shipping costs and lost Gulf flows, while strong US inventories and Strategic Petroleum Reserve releases held WTI down. The difference now is that the pressure on WTI comes from US policy rather than from US supply alone. A policy-driven spread can close as fast as it opened, if the diesel ban is ruled out.
Section 05Which Barrel Indonesia Buys
Indonesia's reference price is the Indonesian Crude Price (ICP), set monthly by the Ministry of Energy. Since 2016 its formula has been Dated Brent plus an adjustment for each crude grade. ICP is what the state budget, production-sharing revenue, and the subsidy bill are calculated on. It does not reference WTI.
The August ICP was $89.43 a barrel, up $7.75 from $81.68 in July. September's figure, due in early October, will be built on a month in which Brent climbed from about $93 in the first week to above $100 from the second week on. The 2026 budget assumed an average of $70.
Domestic output is roughly 570,000–610,000 barrels a day against consumption of 1.4–1.7 million. Indonesia therefore buys most of its oil and fuel abroad, mainly in Asian markets priced off Brent and Middle East grades, and pays in dollars. When Brent stays high, so does that dollar bill, whatever WTI does.
Section 06The Fiscal Arithmetic
The government has chosen to absorb the shock in the budget. Subsidised fuel prices, including Pertalite, are held unchanged through the end of 2026. Government estimates put the cost of each $1 of ICP above the assumption at about Rp10.3 trillion in extra spending, against about Rp3.5 trillion in extra revenue. The net effect is about Rp6.8 trillion on the deficit.
August's ICP sat about $19 above the budget assumption. If that gap held for a full year, it would add roughly Rp130 trillion to the deficit (MetricBase calculation: $19.43 × Rp6.8 trillion). This is an illustration of scale, not a forecast. The actual cost depends on the average ICP across the whole year, which includes cheaper months early in 2026.
The Brent–WTI split matters here in a simple way. When commentators say "oil is back below $100", they are usually quoting WTI. The fiscal gap is set by Brent, which is still above $100. Last week's fall in US crude did nothing for the subsidy bill.
Section 07The Rupiah Channel
The same barrels show up in the external accounts. Indonesia's current account deficit widened to a record $12.5 billion in Q2, 3.3% of GDP, from $3.6 billion in Q1. Bank Indonesia attributed the widening to a larger oil and gas trade deficit as import prices rose. In June alone the oil and gas trade balance was $3.49 billion in deficit, more than offsetting a $3.04 billion non-oil surplus.
That deficit has to be financed, and it is part of why the rupiah sits near 18,000 despite 100 bp of BI hikes in May and June. Reserves are adequate at $146.5 billion at the end of August, or 5.4 months of imports. But reserves fund the gap; they do not close it. On 23 September BI held at 5.75% and chose hedging discounts over a hike. We argue in this week's editorial that this was the right call, because the rupiah is trading on Brent.
Section 08"For Indonesia, the oil price is not the one on the evening news. It is the one on the tanker invoice, and last week those two numbers were twelve dollars apart."
— MetricBase energy desk note, September 2026
What to Watch
These are structural markers, not predictions or investment recommendations.
September ICP (early October)
The first official read on how much of Brent's move above $100 has entered Indonesia's reference price. A print well above August's $89.43 would widen the fiscal gap described in Section 06.
The diesel ban decision
If Washington rules out an export ban, the policy part of WTI's discount should shrink quickly. That would narrow the spread by lifting WTI, not by lowering Brent, and would change nothing for Asian buyers.
US–Iran talks and Hormuz
This is the only path that narrows the spread from Brent's side. A deal that reopens Hormuz and brings freight rates down would cut the premium on the barrel Indonesia actually buys. For the rupiah and the IDX, that is the variable to watch, not WTI.
The practical rule for an Indonesian portfolio: read Brent, not the headline oil price. WTI tells you about US refiners and US politics. Brent, and the ICP built on it, tells you about Indonesia's budget, its current account, and the pressure on the rupiah.
Sources & Data Methodology
WTI and Brent settles and weekly changes: CNBC (25 Sep), Fortune, Trading Economics (first weekly fall in six); Brent in early September from Weekly Brief #20; the 18 September settles are from our Weekly Brief #21. Daily moves: CNBC (21 Sep), CNBC (23 Sep). Diesel ban, freight, US exports, and the $12.02 intraday spread: Reuters via Investing.com, Spreadex. March 2026 spread: S&P Global, EIA STEO (April 2026). ICP formula and August ICP: Katadata, ANTARA. Budget sensitivity and fuel prices: Asia News Network, Indoneo, Tempo. Output and consumption: GK Group. Current account and trade: Indonesia Investments, VOI (June trade). Reserves: ANTARA. BI decision: Bank Indonesia. JCI and foreign flows: Kontan. Rupiah: Kontan. Bitcoin: Crypto.com Exchange BTC/USD daily candles (18 Sep close $80,895; 25 Sep close $84,096).
The weekly spread is computed from reported front-month settles, which can reference different contract months for WTI and Brent; intraday figures are as reported. The Rp130 trillion figure is a MetricBase illustration using the government's per-dollar sensitivity, not an official estimate. Corrections and source challenges are welcome at support@metricbase.org.
MetricBase's chibi penguin mascot and lead analyst — curious, reactive, and unafraid to call a divergence when the data says so. Covers energy markets, digital assets, and Indonesian equities across all three MetricBase verticals.