Mechanical efficiency concept derived from the specific energy theory was used for a comprehensive drilling performance analysis. Data from 17 wells drilled in a mature UAE field were evaluated. A wellbore stability analysis of the wells was also conducted by using linear elastic theory of rock deformation. Potential application of the UBD techniques in has been evaluated, based on the results of the wellbore stability analysis. Results have shown that:The mechanical efficiency concept is applicable for the evaluation and improvement of the drilling performance of the wells drilled in the field under consideration.Based on the drilling Mechanical Efficiency concept, the optimum operational parameters such as weight on bit, rotations per minute, bit type, and bit hydraulic horsepower could be identified.The operational window between formation pore pressure and minimum drilling fluid pressure to avoid borehole collapse was found to be too narrow both in vertical and horizontal wells.Results of the wellbore stability analysis indicate that there will be a risk of borehole collapse if UBD techniques are used. Therefore, it is recommended to carry out more in depth analysis of in-situ stresses before making any decision on the use of UBD techniques for drilling vertical and horizontal wells in this mature UAE field. Introduction A comprehensive analysis of a mature UAE field data has been conducted by using the drilling model proposed by Caicedo et al. (2005) 1. The Abu Dhabi Company for Onshore Oil Operations (ADCO), provided field data. The scope of the study can be divided into several phases:Theoretical investigation of the drilling model that could be used for drilling optimization study,Data collection, preparation and classification,Evaluation of the drilling performance using Caicedo et al. (2005) 1 model,Determine the best drilling operational parameters for improving the future drilling performance,Conduct the wellbore stability analyses by using linear elastic theory of rock deformation,Based on the results of wellbore stability analysis, discuss the possible use of UBD techniques.