Tumors consist of spatially and functionally distinct niches which may result from spatiotemporal variation in oxygen concentration (pO₂) within growing tumors.  Cells located in the periphery of tumors are well nourished by diffusion of oxygen and nutrients from adjacent blood vessels (up to ~ 200 mm), whereas cells located in the center of the tumors are exposed to varying levels of hypoxia.  We have recently shown that up-regulation of certain angiogenic factors (e.g. vascular endothelial growth factor) is likely due to low pO₂ in central hypoxic niches, whereas other angiogenic factors (e.g., interleukin-8) are only partially controlled by this aspect.  However, further investigation with spatiotemporal control of pO₂ in tissues is required to more explicitly clarify the role of pO₂ in angiogenic factor secretion.  In this study, we have designed and explored microfluidic tumor models to recreate and analyze distinct tumor niches by varying pO₂.  Microchannels were embedded within alginate-based 3-D tumor models to allow for spatiotemporal control of pO₂ and subsequent analysis of angiogenic factor secretion.  Our strategy includes: 1) mathematical modeling and experimental approaches to establish design requirements for microfluidic tumors, 2) a lithographic technique to build functional microfluidic structures within alginate hydrogels seeded with OSCC-3 (oral squamous carcinoma cells), 3) confirmation of our ability to control pO₂ with oxygen-sensing microbeads, and 4) characterization of angiogenic factor secretion as a function of spatiotemporal variations in pO₂.