The calculated distance (air line) between Oberhausen-Rheinhausen and Dortmund is approximately 161 miles respectively 259 kilometers.
By car or train, the actual journey to Dortmund is certainly longer, as only the direct route (as the crow flies) between Oberhausen-Rheinhausen and Dortmund has been calculated here.
Air line (approximately)
259 kilometers
140 nautical miles