;XO-19 :Improved version of the XO-6 with a
Pratt & Whitney R-1340-3 engine, one built. ;YO-20 :Similar to the XO-19 with a
Pratt & Whitney R-1690-1 engine, one built. ;XO-21 :Similar to the XO-19 with a
Curtiss H-1640-1 engine, one built, later re-engined as the XO-21A. ;XO-21A :The XO-21 fitted with a
Wright R-1750-1 engine. ;O-19 :Service evaluation aircraft with a
Pratt & Whitney R-1340-9, two built. ;O-19A :O-19 without the 88 US Gallon main fuel tank, one built. ;O-19B :Production version with a
Pratt & Whitney R-1340-7 engine, two machine-guns and modified cockpit, 70 built. ;O-19C :O-19B with tailwheel, ring cowl and minor changes, 71 built. ;O-19D :One O-19C converted as a VIP staff transport with dual controls. ;O-19E :O-19C with extended upper-span wing and a
Pratt & Whitney R-1340-15 engine, 30 built. ;O-21 :O-19 with
Curtiss H-1640 Chieftain engine, one built, one converted. ;YO-23 :XO-19 with a
Curtiss V-1570-1 Conqueror engine, one built. ;Y1O-33 :One O-19B re-engined with a
Curtiss V-1570-11 engine and revised tail surfaces, one converted. ;Y1O-41 :A sesqui-plane conversion of the Y1O-33 with a
Curtiss V-1570-79 engine, one converted. Later modified by
Consolidated Aircraft as their
Model 23 and exported to Mexico. ;Y1O-42 :High-wing monoplane version of the Y1O-41, static test airframe only. == Operators ==