Magnetic and Mossbauer measurements have been used to study the superparamagnetic behaviour of a magnetic fluid containing iron particles. Electron micrographs show the particles to form a Gaussian distribution with median diameter D_p=65 AA, sigma =12 AA whilst magnetic analysis gives the median diameter D_vm=60+or-5 AA at 80K and D_vm=55+or-5 AA at 300K. Superparamagnetic behaviour was evident for the magnetic measurements at both 80 and 300K. The Mossbauer spectrum at 86K contained two lines which were associated with the superparamagnetic iron core and the FeO coating. The FeO line showed no evidence of magnetic ordering when the coating was thin ( approximately=10 AA) but this was apparent when the coating thickness was increased by prolonged oxidation.