The calculated distance (air line) between Olfen and Oer-Erkenschwick is approximately 7 miles respectively 11 kilometers.
By car or train, the actual journey to Oer-Erkenschwick is certainly longer, as only the direct route (as the crow flies) between Olfen and Oer-Erkenschwick has been calculated here.
Air line (approximately)
11 kilometers
6 nautical miles