UPDATE 1-Shell reports Deer Park hydrocracker upset -filing

(Adds details about refinery ownership, type of unit)

HOUSTON, Jane 24 (Reuters) - Shell Oil Co's joint-venture 329,800 barrel per day refinery in Deer Park, Texas, reported a hydrocracker upset on Sunday, according to a notice filed with Texas pollution regulators.

A relief valve on the selective hydrocracking unit released hydrogen sulfide to the atmosphere on Sunday morning, according to the notice filed with the Texas Commission on Environmental Quality. Piping alignments were made to stop the release.

Shell manages operations at the Deer Park refinery, which is a 50-50 joint venture with Mexico's state-owned oil company Pemex. The refinery is the ninth-largest in the United States. Shell is the U.S. unit of Royal Dutch Shell Plc (RDSa.L).

A hydrocracker uses hydrogen to make gasoline and diesel from crude oil. (Reporting by Erwin Seba; Editing by Diane Craft)