Fe, Co and Ni particles were prepared in water/polyoxyethylene-4-laurylether/n-hexane and water/polyoxyethylene-4-laurylether/decahydronaphthalene microemulsions by reduction of metal nitrates dissolved in the water pools of the reversed micelles. The particles were mostly monodispersed with average diameters in the range 8 to 23 nm, as determined by dynamic light scattering (DLS). However, significantly smaller size estimates were obtained using transmission electron microscopy (TEM). The average DLS particle diameters increased with increased average diameter of the reversed micelles, and the diameter of the reversed micelles increased with an increase in the microemulsion water : surfactant ratio and metal ion concentration. The diameter of the reversed micelles was also dependent upon the metal dissolved in the water pool, increasing in the order Ni < Co < Fe; These trends are explained in terms of changes that occur to the microemulsion hydrophilic-lipophilic balance. Preparation of nickel and cobalt sulfides by sulfidation of the metal salt with H2S at low temperature, yielded much larger diameter particles (average diameter 75 nm). Measurement of the activity of the sulfided catalysts showed that the Co catalyst was more active than the Ni catalyst for the hydrocracking of diphenylmethane, and Co was more effective than Fe in reducing coke yield during Cold Lake residue hydroprocessing.