Evaluation of corrosion rates in hard-to-access equipments, such as those found in petroleum production, is still a difficult task. Sensors for corrosion rate evaluation are normally based on sacrifice bodies or in the cathodic reaction that occurs with the oxidation and reduction reactions of the corrosion process. Environmental conditions like temperature, pressure, chemical composition, and pH, are fundamental factors of environment severity and have a direct influence on corrosion rate predictions. In the Petroleum Industry, metallic corrosion may cause premature failure of equipments and fluid leaks, often resulting in expensive maintenance operations and posing safety and environmental risks. This work presents new concepts for fiber optic pH sensors that may be applied for permanent monitoring of petroleum wells. Two measurements principles were evaluated. The first one is based on measurements of refractive index changes in commercial pH indicators. The second solution explores a pH sensitive polymer, whose changes in volume strains a fiber Bragg grating. Experiments reported here show that the second technique has a better sensitivity, particularly under the operation conditions found in oil wells. It also allows the use of multiple fiber optic sensors simultaneously monitoring other physical quantities, such as temperature, pressure, and flow rate, which directly affect corrosion rates. The sensor was tested in acid environment, with special attention paid to temperature, solubility and response time. The sensitivity achieved was better than 0.01 pH units. More experiments still need to be performed in order to produce a prototype that will be testes in real operation conditions in producing petroleum well.