 Malignant biliary obstruction can result from extrinsic processes, such as proximal pancreatic ductal adenocarcinoma or metastatic lesions, or from intrinsic lesions such as cholangiocarcinoma. Malignant biliary obstruction is typically treated endoscopically with placement of either plastic polyethylene or metal biliary stents. Metal stents have a wider diameter than plastic stents, and have been shown to have higher patency rates, but are also 15-40 times the cost of plastic stents. Metal stents with a polymer coating have been developed to prevent tumor ingrowth into the stent, which can lead to stent occlusion. Cost analysis has demonstrated an advantage to the use of metal stents in patients with unresectable disease, or who may achieve operable status following neoadjuvant chemotherapy, while either plastic stents or metal stents are used when patients are deemed to have a surgically resectable lesion. Patients determined to have resectable, or borderline resectable malignancy those who may achieve resectability status following neoadjuvant chemotherapy will receive either plastic, uncovered metal, or covered metal stents in a randomized fashion, while patients determined to have surgically unresectable malignancy will randomly receive either covered or uncovered metal biliary stents. The primary aim of this study is to prospectively evaluate stent occlusion rates in patients presenting with malignant biliary obstruction. Secondary aims of the study will include a cost analysis of each stent type, rate of hospital admission following stent placement, days off of chemotherapy due to procedural complication, and rate of acute cholecystitis associated with stent placement. 