An inlet assembly for a an abatement burner includes: an inlet conduit operable to convey an effluent gas stream to be treated from an inlet aperture via a bore to an outlet aperture for treatment; and a lance conduit operable to convey a fuel gas from a gas inlet aperture via a gas bore to a gas outlet aperture positioned within the bore for mixing with the effluent gas stream, a cross-sectional area of the gas bore increasing towards the gas outlet aperture. In this way, the expansion caused by the increasing cross-sectional area of the gas bore enhances the mixing of the fuel gas with the effluent gas stream which provides for improved destruction and removal efficiencies (DRE), which enables the inlet assembly to be operated with reduced quantities of fuel gas, while still maintaining required levels of DRE.