For the oil industry, leaks in pipelines and other oil and gas infrastructure can be disruptive, expensive and can cause severe damage to the environment. To minimize the damage from leakage, a rapid leak detection is essential. Since pipelines are usually located in the remote areas and buried underground, monitoring for leaks is an issue. This study describes the design and development of the Subsurface Direct Hydrocarbon Remote Sensor leak detection system. The system consists of Direct-C’s proprietary polymer nanocomposite based hydrocarbon leak detection sensor and communication system. Polymer nanocomposite provides, unique approach to the leak detection which detects the presence of the smallest amount of hydrocarbon through a change in the electrical property of the material. The mechanism of this sensing process is described along with the advantages of this technology vs other approaches. These sensors are placed within tubes called “surface access ports”, which are partially buried in the ground next to pipelines at regular intervals. The solution is particularly suited for high consequence areas as the last line of detection near urban areas, water crossings, or other environmentally sensitive areas. The paper also details the third-party validation tests conducted on the system to demonstrate the operation of the system in a laboratory environment using a testing setup representative of underground field conditions. The test setup and conditions are described. During the testing, the leak detection system was exposed to different types of hydrocarbons to demonstrate its capability to detect a large variety of hydrocarbons.  The tests proved that the presented system is successfully able to detect all the leaks generated during the testing program.