Co-annular smoke-free laminar diffusion wick-fed flames of dodecane, aviation bio-paraffins and each blended with various amounts of propylbenzene of 10, 20, 25 vol% have been used to study soot formation. A light extinction method is adopted to determine the total soot volume (TSV) as a function of flame height and fuel mass consumption rate (FMCR). The empirical models have been built to predict TSVs of dodecane/propylbenzene (Do/PB) mixtures and aviation bio-paraffins/propylbenzene (Bio-P/PB) mixtures as the function of two variables of FMCR and concentration of propylbenzene content (%PB). TSVs of Do/PB mixtures and Bio-P/PB mixtures increase with increasing flame height, FMCR and %PB. The effect of flame height, FMCR and %PB on soot formation are respectively expressed as the quadratic, power law and linear functions. At low FMCRs, Bio-P/PB mixtures produce a slightly higher TSV than Do/PB mixtures. In contrast, at high FMCRs, the soot formations of Do/PB mixtures are slightly higher than those of their corresponding counterparts. The differences are argued to be mainly due to the remainder of a small amount of oxygenates in the bio-paraffins. It may be concluded that the aviation bio-paraffins are very similar to dodecane in respect to soot formation. (C) 2019 Elsevier Ltd. All rights reserved.