While extensive experimental testing was necessary prior to the approval, detailed isobutanol combustion models are still inaccurate at engine-relevant conditions, indicating a gap in our understanding of isobutanol combustion. Detailed isobutanol mechanisms typically deviate more from experiments than do models of n-butanol, tert-butanol and sec-butanol. Multiple inter-model comparisons using detailed isobutanol models have showed that at lean, low-temperature conditions the models yield a wide range of ignition timings that deviate from experimental ignition delay measurements in homogeneous charge compression and shock tube setups. One mechanism shows the largest deviations from experiments below 850 K and at fuel lean conditions, indicating that the dependence on O 2 might be incorrectly described. Such shortcomings of isobutanol combustion indicate a need for an improved understanding of isobutanol combustion in combustion regimes in which peroxy radical chemistry is often important. The dominant degradation pathway of peroxy radicals at various temperatures and pressures impacts overall ignition properties such as the negative temperature coefficient region, in which ignition slows with increasing tem- perature.