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The effects of injection pressure and orifice diameter on soot in diesel fuel jets were investigated under quiescent, direct-injection (DI) diesel engine conditions. These investigations were carried out in a constant-volume combustion vessel with complete optical access. The injector used was an electronically-controlled, common-rail injector. Injection pressures between 40 MPa and 190 MPa and orifice diameters between 501.1m and 180 µm were considered. Soot was measured with a line-of-sight laser extinction technique and visualized with planar laser-induced incandescence. Flame lift-off lengths used in the analysis of the soot measurements were determined with time-averaged OH chemiluminescence imaging. The results show that the peak soot in a fuel jet decreases with increasing injection pressure and decreasing orifice diameter. The decrease in soot with increasing injection pressure was linear with increasing injection velocity (i.e., the square-root of the pressure drop across the injector orifice). The decrease in soot with decreasing orifice diameter was such that for the smallest orifice diameter considered (50 μm), no soot was detectable for the ambient gas and injector conditions considered. These direct measurements of soot within a fuel jet, coupled with estimates of the amount of air entrained relative to the amount of fuel injected, confirm that air entrainment and fuel-air mixing upstream of the lift-off length have an important role in determining the soot levels within a diesel fuel jet.