The growth of complex drilling activities worldwide demands reasonable practices to deal with uncertainties related to the wellbore position. The error associated to a measurement has been reviewed in great detail and advanced technology combined with sophisticated modeling allows the industry to manage the risk of wellbore collision incidents. However, there is a huge variety in risk management applied by different companies. Separation or clearance factors are widely used, but a standard has not been defined. This can be blamed on the complexity of modeling uncertainty. The Industry Steering Committee on Wellbore Survey Accuracy (ISCWSA) published several models, suggestions and recommendations, but an explicit standard protocol has not been set. The aim of this thesis is to reduce this lack of clarity and present a tool that can be used to compare ellipsoids of uncertainty and consequently separation distances and factors. A scenario was created that is built on a standard set of wellpaths published by the ISCWSA. Eleven different situations of a reference and an offset well are studied and all assumptions, limitations and calculations are described and analyzed. The results show the variety of calculation methods and can be used to recognize shortcomings and impairments. The suggestions made are based on typical real-world conditions and should therefore be more sensitive than general solutions. In addition to that, the estimation of clearance factors is discussed in detail. It is recommended to use a standard clearance factor that incorporates collision probabilities and allows for separation between shallow and deep depths.