HOUSTON, July 8 (Reuters) - Zinc contamination in the Mars crude oil stream pushed down demand for the flagship U.S. coastal crude, slashing its prices on Tuesday, six traders and an industry source said.

Any challenges to the quality of Mars, a popular offshore grade with U.S. refiners, could further tighten supply along the U.S. Gulf Coast at a time when the lack of heavy Venezuelan barrels has crunched availability.

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Mars traded at a 10-cent discount to crude oil at the Cushing storage hub in Oklahoma, easing from a 75-cent premium on Monday, traders and dealers said.

Shell (SHEL.L) , opens new tab, which operates the Mars platform, said there are multiple operators that produce oil that are then commingled into Mars Crude.

"Results of tests conducted by Shell Offshore Inc have determined that the product that we contribute to Mars Crude does not have any quality challenges," the company said.

The contamination was likely caused by an additive used on a platform, two sources said. Zinc does not typically occur naturally in crude oil.

Running crude with zinc through refineries can lead to corrosion and damage to units.

The Mars platform has been producing around 160,000 barrels per day for the last 12 months, according to research firm Energy Aspects. The grade is delivered to Clovelly in Louisiana.

https://www.reuters.com/business/energy/mars-crude-oil-prices-ease-zinc-contamination-sources-say-2025-07-09/