In what attorneys said was the largest ever single-plaintiff asbestos verdict in U.S. history, a Mississippi jury has awarded $322 million to a former oil field worker who allegedly inhaled asbestos dust while mixing drilling mud.

Thomas “Tony” Brown Jr., 48, worked in the oil fields from 1979 to the mid ’80s as a roughneck on rigs in Mississippi and offshore in the Gulf of Mexico. He sued Chevron Phillips Chemical Co., which sold the drilling mud, and Union Carbide Corp., the manufacturer, for causing him to develop asbestosis, a lung disease caused by asbestos exposure. He is now on oxygen 24 hours a day.

The jury award was for future medical expenses, pain and suffering, and punitive damages. “Although the asbestos was known to cause cancer and lung disease, Chevron Phillips and Union Carbide continued to market these almost 100 percent pure asbestos products long after they knew the dangers,” Allen Hossley, a lawyer for Brown, told The Wall Street Journal.

Both Chevron Phillips and Union Carbide said they would appeal the verdict. “The credible medical evidence introduced at trial clearly demonstrates that while Mr. Brown suffers from shortness of breath, such [a] condition is not attributable to asbestos exposure,” a Union Carbide spokesman told the Jackson Clarion-Ledger.

The companies also contended that because Brown was illiterate and could not read the hazard statement on the drilling mud additives, he was not entitled to argue that they had provided inadequate warnings.

If the verdict is upheld, Brown will be entitled to an amount nearly equal to Union Carbide’s yearly net income, which was $459 million in 2010. Union Carbide is a subsidiary of The Dow Chemical Co.

Asbestos products were used in drilling mud because asbestos is fire-resistant and a strong bonding agent.