A laboratory screening protocol was designed and conducted to test the efficacy of 8 commercial allochthonous bacterial cultures and 2 non-bacterial products in enhancing the biodegradation of weathered Prudhoe Bay crude oil in closed flasks. Three lines of evidence were used to support the decision to progress to field testing in Prince William Sound: rapid onset and high rate of oxygen uptake, substantial growth of oil degraders, and significant degradation of the aliphatic and aromatic hydrocarbon fractions of the weathered Prudhoe Bay crude oil. A product had to enhance biodegradation greater than that achieved with excess mineral nutrients. Experiments were conducted in closed respirometer flasks and shake flasks, using actual seawater from Prince William Sound and weathered crude oil from a contaminated beach. Analysis of the data resulted in the selection of 2 of the 10 products for field testing. Both were bacterial products. Findings suggested that the indigenous Alaskan microorganisms were primarily responsible for the biodegradation in the closed flasks and respirometer vessels. (Copyright (c) 1992 Society for Industrial Microbiology.)