The objective of this paper is to introduce a computationally efficient methodology for the quantification of mixed(inherent and model-form) uncertainties and global sensitivity analysis (SA) in hypersonic reentryflowcomputations. The uncertainty-quantification (UQ) approach is based on the second-order UQ theory, using astochastic response surface obtained with nonintrusive polynomial chaos. The global nonlinear SA is based on Sobolvariance decomposition, which uses polynomial chaos expansions. The methodology was used to quantify theuncertainty and sensitivity information for surface heatflux to the spherical nonablating heat shield of a reentryvehicle at an angle of attack of 0 deg. Three uncertainty sources were treated in computationalfluid dynamicssimulations: inherent uncertainty in the freestream velocity, model-form uncertainty in the recombination efficiencyused in partially catalytic wall-boundary condition, and model-form uncertainty in the binary-collision integrals.The SA showed that the velocity and recombination efficiency were the major contributors to the heat-fluxuncertainty for the reentry case considered. The UQ and SA were performed with three different levels of inputuncertainty in velocity, which revealed the importance of characterizing the velocity with well-defined uncertaintylevels in the study of reentryflows because the variations in this quantity can drastically impact the accuracy of theheat-flux prediction.