Process for producing modified microorganisms for oil treatment at high temperatures, pressures and salinity

A growth process for producing modified microorganisms which are adapted for use in oil treatment comprising:

• a) selecting a plurality of thermophilic microbial strains;
• b) growing said microbial strains in a medium containing crude oil supplemented with carbon sources other than the crude oil and nutrients in addition to the crude oil and the other carbon sources at a selected temperature, pressure and salinity;
• c) isolating the microbial strains that survive from step b and growing them in a medium containing crude oil and amounts of the other carbon sources lower than in step b and at a temperature, pressure and salinity higher than in step b;
• d) repeating step c wherein in each successive step the medium contains a lower amount of the other carbon sources and a higher temperature, pressure and salinity than in each previous step until microbial strains are obtained that are capable of growing in essentially crude oil as a carbon source and at a temperature range from about 70.degree. C. to 90.degree. C., at a pressure range from about 2,000 to 2,500 psi and at a salinity range from about 1.3 to 35%.