USX Corp. said its third-quarter net income...

USX Corp. said its third-quarter net income fell 64%, reflecting weaker earnings by its USX-Marathon Group oil and gas unit and a loss by its U.S. Steel Group.

The Pittsburgh firm’s third-quarter net income fell to $10 million from $28 million a year earlier. Sales fell to $4.65 billion from $4.77 billion.

Marathon’s third-quarter net income fell 26% to $17 million. The steel unit’s loss reflects start-up expenses for the company’s $260- million slab caster at its Mon Valley plant near Pittsburgh. A slab caster converts molten steel into semi-finished products.