In this monograph a Monte Carlo method is applied to the controlled source electromagnetic (CSEM) method for the purpose of characterising the uncertainty in 1D inversion results. Compared to other methods the Monte Carlo approach has an advantage because it provides results which include correlation between all horizontal layers. The monograph gives a detailed description of the development process of the code and the code itself. In addition results obtained from data aquired from synthetic 1D reference models and the Troll West Oil province are discussed.