This work s objective is the development of inspections tools capable to detect and locate small leaks in gas and oil pipelines. Nowadays, many brazilian pipelines are equipped with reliable leak detection systems, but these still can t detect small leaks caused by slow corrosion processes. The most used pipeline inspection technology is the instrumented pigs. The pig is launched inside the pipeline and goes through it detecting dents and corrosions. Two technologies were developed, one for oil pipelines and other for gas pipelines. The pig oil pipeline working principle is based on the register of the pressure variation caused by a leakage. When the pig pass by a leak, the pressure in the middle of the pig drops, generating a characteristic signal. The gas pipeline technology uses the acoustic energy caused by a gas leaks. The main idea is to equip the pig with specials microphones capable to listen the leak sound propagated in the gas. With a good acoustic interpretation of this phenomenon, is possible to detect this event. The biggest challenge is to discriminate the leak signature from the others pipe s noises. Which technology had it prototype manufactured and tested in real oil and gas pipelines with success. Will be shown the theory of which technology, the labs and fields tests results and future proposals.