In microbial enhanced oil recovery (MEOR) technique, microorganisms and/or their products (gases, chemicals) are used in the enhancement of oil recovery. In the present study. MEOR is tested for Garzan (26° API) crude oil, produced from Southeast Turkey. This work consists of shut-in pressure tests and microbial water flooding experiments. In shut-in pressure tests, the oil is placed in a stainless steel cell and a certain amount of microbial solution (Clostridium acetobutylicum) is introduced. During the soaking period, the pressure increase is monitored. Results of the measurements carried out after this stage show that gas (mainly CO2) production by the bacteria decreases the oil viscosity effectively. In microbial flooding experiments, an unconsolidated, preflooded reservoir model is subjected to microbial treatment and then flooded with water under varying conditions. The bacteria used in these experiments were Clostridium acetobutylicum and mixed soil bacteria. When compared with a conventional water flood, the results of microbial runs showed that the residual oil recovery increased more than 100% and the pH of the medium decreased.