In a risk-based approach to cost-effective management of power plant emissions, chemical speciation of Fly ash is required. A quantitative but indirect separation of nickel phases by sequential extraction was undertaken in conjunction with direct analysis of the sulfidic nickel phase by carbon paste electrode voltammetry (CPEV). Four ash samples produced in a laboratory combustion system From burning high- and low-sulfur residual oil at excess O-2 of 1 and 2-3 mol% were studied. The extractions yielded five phases of nickel. The CPEV analysis of sulfidic nickel in the ash and extraction residues was performed in pH 5 acetate. The anodic peak (-0.1 V) unique to Ni3S2. distinguishing it from NiS and NiS2, was found to be absent from these ash samples. The CPEV method was consistent with phase extraction, which showed NISO4 being predominant with very low proportions of suifidic nickel.