The Lower, Middle and Upper Devonian hydrocarbon pools in the Concession NC8A of the Ghadames (Hamada) Basin, NW Libya were re-evaluated by using volumetric estimation based on deterministic method. This applied method has revealed that, the total oil in place "from all Devonian sandstone pools in Concession NC8A" is 36.12MMSTB. This represents 53% of the oil contributed from ElHamra Field (F, I AA and V structures), while a least percentage of only 4.5% is contributed from Emgayet Field (FFF and FF structures). Other Fields; "GG", "LL", "Y", "O" and "A" are contributed 0.8%, 5.5%, 9%, 10% and 20.5% respectively. In the other hand. a total gas in place "from all Devonian sandstone pools in Concession NC8A" is 5.21 BSCF and was estimated to reveal various percentages; 54% is contributed from LL-Field, 30% from F-structure of ElHamra Field, 6% from FFF-structure of Emgayet Field and 3% is contributed from A-Field. The remaining recoverable oil and gas are 14.25 million barrels of oil and 4.12 billion cubic feet of natural gas, 39.5% and 79% respectively of the total Concession NC8A.

In this study the uncertainty in the hydrocarbon estimation can be reduced to a certain extent if additional geological interpretation and 3D modelling of the studied pools are included in the estimation procedures and, consequently, the reliability of the estimates is enhanced. To achieve maximum effectiveness, oil and gas estimation by deterministic method should possess these types of flexibility.