Class 91 may refer to: British Rail Class 91 DRG or DR Class 91 2-6-0T tank locomotives with the Deutsche Reichsbahn: Class 91.0-1: Prussian T 9.2, BLE Nos. 36 to 43, PKP Class TKi2
Class 91.3-18: Prussian T 9.3 Class 91.19: Mecklenburg T 4 Class 91.20: Württemberg T 9
KTM Class 91 South African Class 91-000 CFR (Romanian Railways) Class 91 (now reclassified as class 98 )