The Mad Dog field is located in Southern Green Canyon approximately 150-miles south of New Orleans, in 4400-ft to 6800-ft of water (Figure 1). Mad Dog wells are sub-salt and are drilled to the Lower Miocene at approximately 19000-ft true vertical depth (tvd). The discovery well for the field was drilled in 1998. Drilling in the field has been challenged by "mobile" tar. Tar has been encountered in other deepwater fields; however, other reported tar deposits have not had the mobility of the tar encountered in the Mad Dog area. Extensive work has been conducted in developing the Mad Dog tar mitigation plan and has included characterization of tar, laboratory plunger experiments with Mad Dog tar, tar shoe design optimization, investigation of solvents and catalysts to solidify tar, investigation of downhole pyrotechnic heating, investigation of coating agents and the review of drilling practices. This paper will document the theory on the origin of the tar deposits, steps taken to deal with the tar and experience with the tar. Introduction The Mad Dog spar platform was installed in Green Canyon Block 782 for producing the Mad Dog Field in 2005. To date, two grass roots wells have been drilled from the spar. Drilling operations have been conducted in the central part of the field which encompasses a graben structure, Figure 2. Mobile tar first became evident on the second appraisal well in the central part of the field. (Figure 3). The tar did not substantially affect drilling operations however it did result in lost time due to stuck wireline tools. One of the most severe mobile tar cases occurred when a Southern Flank exploration well encountered tar and was unable to meet the required total depth objective. Another severe mobile tar case occurred in the final pre-drill (pre-Spar) well drilled in the central graben. The well was side-tracked, encountered more tar and met its objective as a less-than-optimal borehole size due to the addition of several casing strings. Development of a detailed tar mitigation plan during installation of the spar rig proved fruitful as the first spar well also encountered tar and managed to deliver the required total depth and completion.