[O iii] spectra of the 10 objects with the broadest [O iii] emission, as measured by the width containing 80 per cent of the line power w₈₀. The spectrum of the [O iii]λ4959,5007 Å region is shown in grey, and the model components (continuum and two or three Gaussians) are shown in red for the 5007 Å line (the fit is performed simultaneously on both lines in the doublet assuming the same kinematic structure). The summed model for both lines of the [O iii] doublet is shown in black. Vertical dashed lines show v₁₀, v₅₀ and v₉₀, so that w₈₀ is encompassed between the left and right lines. The 10 objects shown in the figure have w₈₀ values in the range 2558–3912 km s⁻¹. These values are comparable to the maximal widths found in the Reyes et al. (2008) sample (Zakamska & Greene 2014), but fall short of the extreme values (up to 5409 km s⁻¹) found in high-luminosity red quasars at high redshifts (Zakamska et al. 2016b). Each spectrum is labelled with its plate, fibre and MJD.