A process and apparatus are provided for upgrading steam cracker tars from steam crackers. The invention also relates to a steam cracking process and apparatus for reducing yields of tars produced from steam cracking while increasing yields of higher value products by heating steam cracker tar, in the presence of hydrogen donor compounds, e.g., tetralin. The hydrogen donor compounds can be provided in a hydrogen donor-rich hydrocarbon stream, e.g., light cycle oils, or low sulfur vacuum tower bottoms. The treated tar can be separated into gas oil, fuel oil and tar streams.