The detection of the source of communication and pressure build up in the first or second annuli presents a huge challenge to the industry. Dubai Petroleum has been utilizing an acoustics based logging tool to pinpoint the source of high pressures in the annuli of its gas lifted oil producers and water injectors in its offshore operations. This paper presents a description of the technology and the findings from Dubai Petroleum's experience on several case histories. An ultrasonic leak detection tool has been developed for down-hole applications, to take advantage of the unique properties of ultrasound energy propagation through various media. This data acquisition equipment has been developed to allow continuous logging operation on conventional electric line cable or memory mode on slick line. The movement of fluids across a failed barrier creates turbulence creating high frequency ultrasound waves that are detected by the tool sensor. This new tool is different from the conventional noise logs as its highly customized multiple sensitivities enable the detection of leaks as small as 0.02 Liters per minute with an accuracy of 1 Inch in the production tubing, casing and other completion equipment. It is also less prone to disturbances from distant noise sources. The successful experience gained by Dubai Petroleum in utilizing this technology has confirmed that ultrasonic based well leak detector technology can accurately detect very small tubing and casing leaks. Introduction: The challenges related to well integrity issues are a major concern in a growing inventory of aging wells all over the world. Interventions to repair the leaking wells or closing and abandoning wells have led to high operating cost, low overall oil recovery, and in some cases unsafe operation. The reasons why leakages occur can be different, and finding the causes is a very complex task. Internal and/or external corrosion is probably the most common cause of leaks in aging wells completions. The varying stress/strain regimes a well is subjected to during its service life can lead to failure of one or more of its safety critical elements: tubulars, production packers, down hole safety valves, SSDs, mandrels etc.