An in hole fluid motor for driving a drill bit utilizing the circulation of drilling fluid to drive the motor, having a sealed bearing assembly. The bearing assembly has a hollow, rotary drive shaft disposed within a tubular relatively stationary housing with radial bearings and thrust bearings disposed between the drive shaft and housing. Sealing structures are provided between the drive shaft and housing in axially spaced relation with the bearings disposed in a chamber between the sealing structures and lubricated by a lubricant confined by the sealing structures and pressurized through a diaphragm by the pressure of fluid externally of the housing in the drill hole. One of the sealing structures has a pair of clean fluid reservoirs separating the bearing lubricant from the drilling fluid in the housing by a pair of sealing devices, one between the bearing lubricant and a first of the clean fluid reservoirs and the other between the first and the second clean fluid reservoirs. In the two forms shown, drilling fluid in the housing pressurizes the second reservoir. In one of these forms, drilling fluid in the housing also pressurizes the first reservoir, and in the other form, lubricant in the bearing chamber pressurizes the first reservoir. The pressure difference between motor fluid upstream of the bit and in the drill hole is sealed by a high pressure seal operating in the clean fluid provided in the reservoirs, and the total volume of the drilling fluid circulates through the bit nozzles.