Union Pacific says crews working overnight have cleared 17 of 27 derailed coal cars in Wagoner County.
The coal train derailed northwest of Okay Wednesday afternoon.
The railroad says the remaining cars are expected to be cleared by Thursday afternoon.
Union Pacific says crews have begun working on repairing 1,500 feet of damaged track and expect to re-open the section sometime early Friday.
The railroad says the cause of the derailment has still not been determined. In a statement, Union Pacific says the "train's event data recorder is being reviewed and items collected from the scene are being analyzed."
Union Pacific says it's re-routed its trains along alternate tracks in eastern Oklahoma.