Blood oxygen level dependent (BOLD) MRI is used to provide information on tumor oxygenation. However, the measurements are susceptible to blood flow changes, which often occur during hyperoxic gas challenge. This study investigated the extent of flow sensitivity by comparing BOLD measurements with and without flow suppression using two orthotopic lung xenograft tumor models. Flow suppression was found to affect multiple measurements including ΔSI(%) and R2*. The range of discrepancy was smaller in R2* than the ΔSI(%). High similarity was found in spatial patterns. ROI and spatial pattern analysis showed higher sensitivity to flow in A549 tumors than H460 tumors.