This is an example of the application of a combination of the latest technologies to assure the early detection of leaks in underground river crossings and environmentally sensitive zones of gas and oil fields operated by Perez Companc. One of the most important environmental impact risks within our oil and gas production operations is the potential possibility of spilling hydrocarbons to our rivers. Tens of cities, that take drinking water for the human consumption or that use the resource as a means of recreation and thousands of hectares irrigated for the maintenance of the agricultural and cattle-raising activity, gives significance to these risks. To reduce these risks in the 260 mts. long underground crossing of the Neuquén River, located in the Neuquén province, Argentina, an annular casing system was devised. This space is pressurized with nitrogen to a level over that of the pipeline. Any abnormal condition is detected through the supervision of both the casing and pipeline pressures with a very simple control logic implemented in a remote transmission unit (RTU) In case of a leak, or defect in any system, the RTU is responsible for closing pipeline valves and sending remote and local alarms to the field’s SCADA system. The RTU is connected to the Supervision, Control and Data Adquisition (SCADA) System through a digital Spread Spectrum radio link. The simplicity of the control logic and the pressure transmitters and communication system reliability assures an interesting cost-benefit relationship.