[en] The use of in situ gamma spectrometry is increasing nowadays thanks to its fast (immediate) results, good detection limits (comparable with laboratory results), and a good representativity of the average of the activity levels over the field under study. The standard analysis generally used is described in ICRU 53. This paper presents new developments for the data analysis of in situ gamma spectrometry data. This new analysis is based on intensive Monte Carlo simulations of the source geometry, now possible due to the large availability of high performance computers. The Monte Carlo and the analysis are separated, the result of the first being stored on a huge database containing the history, all the way back to the initial particle (kinematic position, energy) for all successfully simulated particles. At analysis time queries corresponding to the actual measured field are sent to the database. This method has been successfully applied to : The analysis of real in situ data corresponding to situations where the standard analysis is not applicable. The calculation of conversion factors required by in situ gamma spectrometry following the 96/29/EURATOM directive. Understanding the origin of fluence found in real situations. In the short term, this approach should lead to an operational tool