NOVELTY - Degradation of an oil sludge in a pipeline, involves: introducing a microbial mixture comprising a Pseudomonas sp. and a nutrient medium into the pipeline such that the microbial mixture contacts the oil sludge, where the Pseudomonas sp. is selected from Pseudomonas aeruginosa, Pseudomonas fluorescens, and any combination.    USE - The methods and microbial mixture are useful for the degradation of an oil sludge in a pipeline, for preventing a build-up of an oil sludge in a pipeline, and for pretreating crude oil (all claimed).    ADVANTAGE - The methods and microbial mixture provide inexpensive, non-toxic, economical and environment-friendly way of degrading oil sludge in pipelines and storage tanks. Moreover, the microbial mixtures may also be used to reduce wellbore skin damage. Injection of the microbial mixture in the wellbore may degrade the deposited wax near the wellbore and reduce the viscosity of the oil, making it easy to flow. In addition, the microbial mixture may also be used to remove tank bottom sludge, and the microbes may degrade heavier hydrocarbons in the sludge to lower alkanes and fatty acids, and make the sludge flowable. Further, the microbial mixture may as well be used in de-emulsification of oil-water emulsion in oil and gas facilities.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for: (1) a pipeline comprising an oil sludge, a microbial mixture comprising a Pseudomonas sp. and a nutrient medium disposed within the pipeline, where the microbial mixture is in contact with the oil sludge, and where the Pseudomonas sp. is selected from P. aeruginosa, P. fluorescens, and any combination; (2) a biofilm comprising a Pseudomonas sp. and a nutrient medium, where the nutrient medium comprises potassium dihydrogen phosphate (KH2PO4), sodium hydrogen phosphate (Na2HPO4), ammonium chloride (NH4Cl), sodium chloride (NaCl), glucose, magnesium sulfate (MgSO4), or any combination; (3) a method of preventing a build-up of an oil sludge in a pipeline, which involves: providing an oil flow in the pipeline; and introducing a microbial mixture comprising a Pseudomonas sp. and a nutrient medium into the pipeline, where the Pseudomonas sp. is selected from P. aeruginosa, P. fluorescens, and any combination; and (4) a method of pretreating crude oil, which involves: contacting crude oil with a microbial mixture comprising a Pseudomonas sp. and a nutrient medium, where the microbial mixture degrades about 70-99% of an oil sludge present in the crude oil in a period of 1-3 days, and where the Pseudomonas sp. is selected from P. aeruginosa, P. fluorescens, and any combination.