We report magnetotransport measurements of InSb/Al1-x In x Sb modulation doped quantum well (QW) structures and the extracted transport $({\tau }_{{\rm{t}}})$ and quantum $({\tau }_{{\rm{q}}})$ lifetime of carriers at low temperature $(\lt 2\,{\rm{K}}).$ We consider conventional transport lifetimes over a range of samples with different doping levels and carrier densities, and deduce different transport regimes dependent on QW state filling calculated from self-consistent Schrödinger–Poisson modelling. For samples where only the lowest QW subband is occupied at electron densities of $2.13\times {10}^{11}$ cm−2 and $2.54\times {10}^{11}$ cm−2 quantum lifetimes of ${\tau }_{{\rm{q}}}\approx 0.107$ ps, and ${\tau }_{{\rm{q}}}\approx 0.103$ ps are extracted from Shubnikov–de Haas oscillations below a magnetic field of $0.8$ T. The extracted ratios of transport to quantum lifetimes, ${\tau }_{{\rm{t}}}/{\tau }_{{\rm{q}}}\approx 17$ and ${\tau }_{{\rm{t}}}/{\tau }_{{\rm{q}}}\approx 20\,\,$are similar to values reported in other binary QW two-dimensional electron gas systems, but are inconsistent with predictions from transport modelling which assumes that remote ionized donors are the dominant scattering mechanism. We find the low ${\tau }_{{\rm{t}}}/{\tau }_{{\rm{q}}}$ ratio and the variation in transport mobility with carrier density cannot be explained by reasonable levels of background impurities or well width fluctuations. Thus, there is at least one additional scattering mechanism unaccounted for, most likely arising from structural defects.