Reservoir fluids of the White Tiger oil field (Vietnam) were studied for the purpose of the development of the combined physicochemical and microbiological technique of enhanced oil recovery. The reservoir conditions of the oil field facilitate the formation of numerous and versatile biocenosis represented by microorganisms of the Pseudomonas, Bacillus, Arthrobacter, Micrococcus, Nocardia, Brevibacterium, Flavobacterium, etc. genera. These microflora positively respond to the introduction of an oil-displacement composition at a concentration of up to 5% as a nitrogen nutrient source. The active multiplication of the microflora is accompanied by the oxidation of saturated White Tiger petroleum hydrocarbons: the proportion of C(10)-C(15) and C(21)-C(26) decreases, the proportion of the isoprenoid hydrocarbons pristane and phytane increases, and the isoprenoid factor increases from 0.54 in the initial oil to 1.65 after its biodegradation. A simulation of the displacement of viscous oil with the use of the detergent composition and hydrocarbon-oxidizing microflora has shown a 12-14% increment in the oil-displacement efficiency, where the contribution of microflora is estimated at 4-6%.