On May 4, the last U.S.-bound oil tanker to have passed through the Strait of Hormuz docked in Long Beach, CA. Since the strait’s effective closure, shipments that had already passed through the strait helped delay the worst domestic supply shocks. This milestone marks the tail-end of an important supply chain that, as of mid-June, remains difficult to fully re-establish. The U.S. is a net energy exporter, which might suggest that disruptions to imported energy supplies pose only limited risks. In theory, exported fossil fuels could be redirected to produce the chemical products most affected by the closure, like urea, ammonia, and ethylene. However, the reality is more complicated.
How refinery feedstocks evolved
Enabled by new technologies and increasingly interconnected global supply chains, the feedstock requirements for chemical processes like refining, ethane steam cracking, fluid catalytic cracking (FCC), and plastics manufacturing have become more demanding over the last century. Running these systems on off-spec feedstocks can often introduce contaminants, fouling, safety hazards, and other operational issues. Historically, optimization often narrows acceptable feedstock and operating ranges, particularly when systems are designed around stable inputs and supply chains.
In the refining sector, for example, decades of investment decisions continue to shape which feedstocks can be processed economically. Before the 1970s, most American refineries processed low-sulfur, low-density domestic crude. These systems were less efficient and relied on fewer catalyst-intensive conversion processes, making them less sensitive to some forms of feed variability. However, spurred by the OPEC oil crisis and fears about dwindling supplies of light, sweet crude, eyes turned to the large reserves of heavier, dirtier crude found in Venezuela, Mexico, and the Middle East. U.S. refineries pioneered technologies that made them especially capable of refining difficult-to-process crude. Later, the shale boom allowed the U.S. to produce more light, sweet crude, creating a mismatch between production and refining capacity. It has been profitable to import heavier crude while exporting easier-to-refine crude for a premium. After decades of this trend, the U.S. has built up a glut of light, sweet crude, contributing to an all-time oil export record in May 2026 (1).
This transition toward heavier, sourer crude contributed to increased refinery complexity, which can be quantified using the Nelson Complexity Index (NCI). While increasing complexity can expand the range of crude oils a refinery can process, it can also encourage optimization around feedstocks that provide the greatest economic return. Early refineries had NCI complexity factors around 1. Today, U.S. refineries boast the highest complexity factors in the world, with Gulf Coast refineries averaging above 12. Infrastructure that relied on this globalized system has made it economically and operationally difficult to substitute heavy, sour crude for lighter feeds.
Throughout the 20th century, it made sense for processes to maximize efficiency. Now, the challenge is no longer simply to build the most efficient process, but to build processes that remain viable when feedstocks change.
Why feedstock flexibility matters now
Increasing feedstock flexibility is one of the ways the U.S. chemicals industry can become more resilient while supporting sustainability goals. If processes can be retrofitted to accept a wider variety of sustainable drop-in feedstocks, blending fossil-fuel-derived feeds with biobased and recycled feedstocks may reduce overall carbon intensity. While past technologies may have been flexible yet inefficient, these new technologies allow for a healthier balance between resilience, optimization, and sustainability.
Around the world, systems that rely on global supply chains are struggling to secure minimum feedstock requirements. Due to the strait’s closure, some East Asian steam crackers, unable to import naphtha, have declared force majeure, while some fertilizer manufacturers in Asia and Africa have shut down due to natural gas shortages. As disruptions to global supply chains become more frequent, flexibility becomes increasingly valuable. Fortunately, several emerging technologies are addressing this challenge.
Technologies expanding feedstock options
Recent CEP coverage has highlighted several examples of such technologies. Last month’s feature from Linde (pp. 27–32) describes how oils derived from waste plastics can be blended with conventional cracking feeds to produce chemical products like ethylene and propylene. Other examples include the biofeedstocks featured in the May 2026 Special Section on the Circular Bioeconomy (pp. 15–34), which highlighted biobased chemical products derived from specialized energy crops, forest residue, microalgae, and more.
In refining, co-processing of blended renewable and conventional feeds is becoming increasingly relevant as companies work toward environmental goals and adjust to higher oil prices. New technologies make co-processing an attractive option, as they allow some refineries to accept more diverse feeds with minimal changes to existing infrastructure. In many cases, the goal is no longer to redesign the entire plant, but to redesign feedstocks to pass through existing systems.
Modern processes rely on lean manufacturing and supply-chain optimization, making them sensitive to global instability. At the same time, renewable feedstocks remain costly, recycled feedstocks require infrastructure investment, and existing chemical processes require time, capital, and certainty in order to retrofit. As engineers look toward the future, building processes to be resilient and flexible could give us the chance to shape a more sustainable foundation.
- Somasekhar, A., and G. Mccartney, “US Crude Exports Hit Record High in May as Iran War Tightens Global Oil Supplies,” Reuters, https://www.reuters.com/business/energy/us-crude-exports-hit-record-high-may-iran-war-tightens-global-oil-supplies-2026-06-01 (June 1, 2026).
This article originally appeared in the Emerging Voices column in the July 2026 issue of CEP. Members have access online to complete issues, including a vast, searchable archive of back issues found at www.aiche.org/cep. Learn more about AIChE membership.
