Study of Bevacizumab in Combination With 5-FU, Oxaliplatin and External Beam Radiation Followed by Gemcitabine and Bevacizumab for Locally Advanced Pancreatic Cancer

* The combination of all three drugs and radiation treatment has never been given to people before, therefore, we are going to add just one additional drug at a time for safety reasons. * The first group of participants (3-4) who enroll on the study will receive 5-FU, radiation therapy with the added drug oxaliplatin, this is called Regimen level 1. If these participants have few or easily manageable side effects, then another group of participants will be enrolled and will receive 5-FU, radiation, oxaliplatin with the addition of bevacizumab this is called Regimen level 2. * The combination of study drugs and radiation will last about 6 weeks, this 6 week period is called a cycle 1. * Regimen Level 1 will receive the following: oxaliplatin intravenously on days 1, 8, 15, 22, 29, and 36; 5-FU infused by a continuous infusion on days 1-5, 8-12, 15-19, 22-26, 29-33, and 36-38; radiation therapy Monday-Friday to complete on day 38. * Regimen Level 2 will receive the following; bevacizumab intravenously on days 1, 15, and 29; oxaliplatin intravenously on days 1, 8, 15, 22, 29 and 36; 5-FU infused by continuous infusion days 1-5, 8-12, 15-19, 22-26, 29-33, and 36-38; radiation therapy Monday-Friday to complete on day day 38. * The following are tests and procedures that will be performed during cycle 1: physical examination; blood work, urine sample. perfusion CT scan on day 12 (for those participants enrolled at Massachusetts General Hospital). * At the end of cycle 1, CT scans will be performed to evaluate the participants disease status before they receive combination gemcitabine and bevacizumab. If the scans show the tumor has reduced in size and can be surgically removed, then surgery will be scheduled and the patient will receive gemcitabine and bevacizumab about 4 weeks after the surgery. If the scans show the tumor can not be removed, the patient will receive the gemcitabine/bevacizumab combination about 4 weeks after completing cycle 1. * Cycles 2-5 consist of: gemcitabine given intravenously on days 1, 8, and 15 every 28 days; bevacizumab given intravenously on days 1 and 15 every 28 days. During cycles 2-5 the following tests and procedures will be performed: physical examination including vital signs on day 1 and 15 of each cycle; blood work on days 1, 8 and 15 of each cycle; a urine sample on day 1 of each cycle; CT scans will be done every 2 cycles. * It will take about 7 months to complete the study treatment (longer for those who have surgery after Cycle 1).