Abstract: A multi-stage ferrofluid seal incorporates a ferrofluid reservoir for extending seal life. The reservoir is located between seal stages and contains a quantity of ferrofluid sufficient to replace ferrofluid in the seal stages which is lost due to evaporation or contamination. The seal is designed to withstand a pressure drop between a high pressure area and a low pressure area and the location of the reservoir is selected so that the pressure capacity of the seal stages between the low pressure area and the reservoir is sufficient to withstand the entire pressure drop. The pressure capacity of the seal stages between the high pressure area and the reservoir is less than the entire pressure drop. Failure of the seal stages between the reservoir and low pressure area causes failure of the seal stages between the reservoir and the high pressure area.