Uncommon Cracking Demand at Petchems Amid Tight Octane Market Lifts Mont Belvieu Isobutane to 27-Month Price High

Two petrochemical majors along the U.S. Gulf Coast have started using isobutane as a cracking feedstock, OPIS has been informed.

This atypical stream of demand is adding to conventional summertime consumption at U.S. refiners and is underpinning a consistently strong start to August for the Mont Belvieu isobutane price, a well-placed contact in the chemical industry said.

With one-third of the trading month gone, isobutane’s physical price and its price premium over normal butane are both steady at levels last seen in May-June 2024.

Isobutane is a relatively illiquid commodity with a reputation for being controlled by “a few strong hands” in the bellwether natural gas liquids trading and storage hub located 33 miles east of downtown Houston. Against this backdrop, seasoned trade watchers advised OPIS to exercise some skepticism while addressing its current price strength.

However, sources suggested cracking demand from the two petrochemical operators — a standalone chemical company which no longer has its legacy refining assets, and an integrated international oil major active in both refining and chemicals — is one probable reason for this month’s price behavior.

OPIS was unable to get comment from the two firms involved.

The reported demand from these firms is ultimately said to align with the overall state of the U.S. unleaded gasoline market, which is currently beset with dwindling inventories and thinner imports.

In particular, tightness in the octane market, which has resulted in a bigger price premium commanded at gas stations by premium unleaded gasoline over regular unleaded, is another telltale explanation for the high isobutane price, sources said.

According to OPIS data, isobutane traded out of Enterprise Products Partners caverns in Mont Belvieu was priced on August 10 at $1.41/gal, the highest value since the $1.4125/gal reported on May 8, 2024.

Normal butane on August 10 was priced at $1.01/gal. The resulting isobutane premium of 40cts/gal was the highest seen since 40.3125cts/gal on June 4, 2024.

Isobutane’s premium over normal butane ranged in the 10-15cts/gal in the first half of July, rising beyond 20cts/gal in the last week of the month and beyond 30cts/gal on July 31. It has stayed above that handle since then, and at or above 40cts/gal since August 6.

Isobutane began trading on Tuesday morning at $1.42-$1.43/gal and normal butane at $1.00-$1.005/gal.

U.S. liquefied petroleum gas production is propane-centric, and both butanes are relatively less liquidly traded. Of the two, isobutane almost has boutique status.

Isobutane has higher-valued markets compared with normal butane, and so enjoys a structural premium over the latter as a general principle. This premium tends to widen in warm-weather months and narrows in autumn and winter.

Isobutane is used as feedstock in alkylation units at refineries, which traditionally are its biggest stateside consumers. Alkylation units react isobutane with propylene or butylene to make alkylate. Alkylate is a high-quality gasoline blendstock that boosts octane while maintaining low evaporative emissions. The latter is a necessary attribute for the summer-grade gasoline mandated by U.S. regulators.

Normal butane is also reasonably high in octane, but its higher vapor specifications mean it has better demand in fall and winter, when U.S. gasoline emission standards are looser.

As would be the case in any normal year, normal butane is currently dealing with the end of winter blending, while isobutane is at the peak of its own demand season. This fundamental factor explains the presence of a stronger premium.

The Iran war has added a wrinkle this year. Energy Information Administration data for the week ended July 31 reported finished gasoline inventories of 209.7 million bbl, 7.66% lower than the 227.1 million bbl reported for the corresponding week in 2025.

This drop is largely due to a drying up of gasoline imports. Raw EIA data show aggregate inflows averaged around 507,000 b/d year-to-date through July 31 compared with around 647,000 b/d in calendar 2025.

With domestic demand reasonably steady this summer, U.S. refiners currently are running at close to maximum capacity.

Alkylate imports from India could also be showing signs of slowing, and this could have a bearing on stateside isobutane pricing, one trader suggested last week.

Against this backdrop, another trader commented: “[The isobutane spike is due to] lot of demand. Must be alkylate pricing and premium gasoline … refineries are buying with both hands.”

This source’s mention of alkylate pricing is linked with an outsized increase in the retail price of premium unleaded gasoline since the Iran war began. Premium unleaded at U.S. gas stations currently is priced at nearly a dollar a gallon higher than regular unleaded, according to retail data.

This factor is likely linked with isobutane’s unaccustomed cracking demand at petrochemical firms, the chemical industry source said.

Propane and normal butane are more commonly used as petrochemical feedstocks. Use of isobutane for this purpose is not generally preferred. However, the two majors may be cracking isobutane to produce isobutylene, the expert suggested.

Isobutylene is also used to produce alkylate. It also produces methyl tertiary butyl ether (MTBE), another component that allows refiners to enhance octane values in their gasoline blends.

MTBE is no longer used in U.S. gasoline blending because of environmental concerns and the sway of ethanol, which has replaced MTBE as a primary oxygenate and octane enhancer. But MTBE is widely used in the rest of the world to boost octane content in gasoline. America remains a prolific MTBE exporter, with Mexico among its primary markets.

Global gasoline economics currently are also challenged, thanks to Ukraine’s attacks on Russian refining infrastructure, problems at European refiners and a general disruption of waterborne trade flows. The two U.S. petrochemical firms’ purported efforts to maximize the octane pool by all means feasible make sense in this environment, he said.

Nonetheless, this contact as well as NGL futures markets expect the isobutane price to normalize at the start of autumn.

U.S. driving season will end at the Labor Day weekend, and winter gasoline will gradually replace summer gasoline in refiners’ production slates beginning in September. Against this backdrop, Mont Belvieu isobutane for September was seen physically traded in Mont Belvieu at 20cts/gal below August on August 7.

Forward price curves for isobutane and normal butane published daily in the OPIS NGL Forwards Report also show a sharp narrowing in the isobutane-normal butane spread over the final two quarters.

Data published in the August 10 NGL Forwards Report projected Mont Belvieu normal butane to hold steady around $1.00/gal between September 2026 and February 2027. Isobutane was projected to decline from $1.18/gal in September to $1.00/gal in February.

–Reporting by Rajesh Joshi, rjoshi@opisnet.com; Editing by Alan Lammey, alammey@opisnet.com