Hypoxia (low levels of oxygen) is an important biomarker in many solid tumors, as it is responsible for promoting tumor angiogenesis and resistance to radiotherapy. Hypoxia can be indirectly monitored by measuring levels of deoxyhemoglobin with MRI, using either R2* or quantitative susceptibility mapping (QSM). We compared the two methods for brain tumor and hypoxia imaging in a mouse model of glioblastoma. We found that both methods were sensitive at detecting a decrease in deoxyhemoglobin due to 100% oxygen. However, QSM provided better anatomical information and was better at detecting tumor heterogeneity. QSM is a promising tumor imaging method.