This paper will discuss the findings from a field trial to evaluate the reliability of a retrofitted acoustic data acquisition system in an onshore well in Qatar for a three month period. The technology allows downhole data to be transferred from multiple locations in the well tubing to the wellhead utilizing acoustic waves. From the wellhead, the data is transmitted to engineers PC through a satellite communication system. This technology eliminates the need for expensive hardware or fiber optic cable used in the conventional downhole monitoring systems. The field trial was successfully completed after 111 days of continuous data gathering and monitoring. All P/T gauges and the acoustic data transmission devices installed in the well performed excellently. The objectives of the trial were achieved. We not only were able to collect the downhole pressure and temperature data for well performance analysis but were also able to define the flow patterns (such as the slugging effects) occurring in the well due to changes in bottomhole pressure. This system can be deployed as a temporary installation retrofit in the existing wells utilizing conventional wireline units, or permanently as part of the well completions for monitoring well performance for reservoir management or well performance monitoring purposes. The trial did not cover evaluation of the system under permanent installation mode as part of the well completion. Permanent installations can be considered once more long term experience has been gained from retrofit applications. IT involvement to provide support and the data transmission link is very essential. The paper will describe the overall system, illustrate the quality and accuracy of real time data obtained during the trial and its utilization for well and reservoir performance evaluation purposes. Introduction Completed wells and producing fields often develop problems that were not foreseeable at the completion design stage. When wells, without permanent downhole pressure monitoring, experience a surface pressure decline combined with reducing or varying production rates, surface production data alone may be misleading. The traditionally accepted diagnostic procedure would be to perform static and flowing gradient surveys but that can show only a snapshot of the wellbore conditions. Indeed, if the well is slugging, a conventional gradient survey may in itself create changes in the wellbore conditions and lead to erroneous assumptions. What may be required is to monitor the downhole gradient over an extended period, without continuously disturbing the well by repeated wireline intervention. A national oil company, in the Middle East, operates an established oil / gas producing field, with water injection pressure maintenance. One of the wells died for no obvious reason. After side tracking and re-completing the well, production was resumed but, after four months, the well died again. Static gradient surveys were performed one month and six months after ceasing production, which showed that the well was slowly regaining pressure but still would not flow. With recent advances in the reliability of acoustic data transmission systems, improved data transmission rates and longevity of battery operated devices, the technology now exists to retrofit existing completions with permanent or semi-permanent downhole sensors and transmit the recorded data to the surface completely wirelessly. The data transmitted may be any parameter that can be recorded downhole, such as fluid density, capacitance, viscosity, sand detection, corrosion monitoring or, as in this trial, pressure and temperature. In addition, as the communication is two-way, the system can be used to control downhole devices, such as valves, sliding sleeves and bottom hole samplers. A proposal was made to the client to demonstrate the capabilities of this system in this well by installing pressure and temperature gauges and acoustic relay tools temporarily in the well for a three month trial. The purpose of the trial was to allow the client to evaluate the system prior to considering it for wider application in new and existing completions.