Tumor maintenance relies on continued activity of driver oncogenes, although their rate-limiting role is highly context-dependent. Oncogenic Kras mutation is the signature event in pancreatic ductal adenocarcinoma (PDAC), serving a critical role in tumor initiation. Here, an inducible KrasG12D-driven PDAC mouse model establishes that advanced PDAC remain strictly dependent on KrasG12D expression. Transcriptome and metabolomic analysis indicate that KrasG12D serves a vital role in controlling tumor metabolism through stimulation of glucose uptake and channeling of glucose intermediates into the hexosamine biosynthesis and pentose phosphate pathways (PPP). These studies also reveal that oncogenic Kras promotes ribose biogenesis. Unlike canonical models, we demonstrate that KrasG12D drives glycolysis intermediates into the non-oxidative PPP, thereby decoupling ribose biogenesis from NADP/NADPH-mediated redox control. Together, this work provides in vivo mechanistic insights into how oncogenic Kras promotes metabolic reprogramming in native tumors and illuminates potential metabolic targets that can be exploited for therapeutic benefit in PDAC. Citation Format: Haoqiang Ying, Hailei Zhang, Jonathan L. Coloff, Haiyan Yan, Wei Wang, Shujuan Chen, Andrea Viale, Hongwu Zheng, Ji-hye Paik, Carol Lim, Alexander R. Guimaraes, Alec C. Kimmelman, Eric S. Martin, Jeffery Chang, Aram Hezel, Samuel R. Perry, Jian Hu, Boyi Gan, Yonghong Xiao, John M. Asara, Ralph Weissleder, Y. Alan Wang, Costas A. Lyssiotis, Lynda Chin, Lewis C. Cantley, Ronald A. DePinho, Sujun Hua, Gerald C. Chu, Eliot Fletcher-Sananikone, Jason W. Locasale, Jaekyoung Son. Oncogenic Kras maintains pancreatic tumors through regulation of anabolic glucose metabolism. [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Progress and Challenges; Jun 18-21, 2012; Lake Tahoe, NV. Philadelphia (PA): AACR; Cancer Res 2012;72(12 Suppl):Abstract nr A101.