U.S. petrochemical steam cracker margins have been transformed almost overnight by the Iran war. As shown in the daily margin chart on the right below, margins for ethane, propane, and normal butane (red dashed oval) have surged to their highest levels relative to natural gasoline (light naphtha) since 2014 — a development that stands out even against the long-term annual record on the left, which includes the exceptional 2021 post-Covid spike when all feedstock margins rose together.
The numbers tell the story clearly. Before the war, daily margins were running at roughly 10 c/lb for ethane, 7–8 c/lb for propane, about 1.7 c/lb for normal butane, and around -7 to -10 c/lb for natural gasoline. By early April, ethane had climbed to ~25 c/lb, propane to ~25 c/lb, and normal butane to ~22 c/lb — while natural gasoline deteriorated further to -14 to -18 c/lb. The spread between ethane and natural gasoline, which was running around 15–18 c/lb before the war, reached as high as 49 c/lb in mid-March and remains in the 38–44 c/lb range.
