AGOCO is one of Libyan NOC affiliated companies; decide to pioneer the introduction of a new way of drilling horizontal wells in the Sarir C – North field. As one of the conclusions from the rock strength and wellbore stability undertaken on C- North core was that in order to maintain wellbore stability at such low reservoir pressure, any horizontal drilling in member 5-AA must be undertaken using controlled pressure drilling methods that will require an Under-balance drilling Unit. The main objectives was to drill the horizontal reservoir section to TD at 10767 ft eliminating or minimizing lost circulation where no drilling time would be lost due to cure losses, also to reduce the formation damage. The C-349 H well was the first UBD horizontal well drilled by AGOCO. The paper discusses the objectives, planning, and the performance of horizontal UBD well as the first well drilled by AGOCO.