The micro-sonde well logging system utilizes miniaturized data logging devices, which are released at the bottom of a well and record downhole parameters whilst being transported by fluid flow to surface. The μSonde capsules are designed to be small enough to pass restrictions without obstructing the flow path. Each sonde is activated when launched and thereafter records sensor measurements to a memory. Typical measurements include pressure, temperature, motion and fluid electrical properties. Upon reaching surface, wireless communication transfers the recorded data for analysis. For production wells a magazine carrying μSondes is deployed to the bottom of the well and thereafter, based on predetermined well conditions and/or time intervals, the sondes are released. For drilling operations, the μSonde storage magazine is deployed together with the bottom hole assembly. The sondes are constructed from low density materials such that their effective density can be matched to the well fluid. Applications and design requirements for the μSonde well logging system have been investigated for drilling operations and production well surveys. The development of the micro-sonde (μSonde) well logging system is supported by the Research Council of Norway' Petromaks 2 Ground breaking technology research program.