The Oligocene sedimentary succession in Gialo Filed, NC59 Concession, SE Sirt Basin, Libya consists of mixed carbonate siliciclastic sedi-ments. The studied succession includes Diba and Chadra rock units which have very good reservoir characteristics in the studied conces-sion. The main objectives of the present work are to evaluate the petrophysical parameters of the Oligocene succession using the available wireline logs from well A13 _NC 59. The Oli-gocene facies is mostly clean with some quartzose sandstone, carbonate-cemented sand and limestone intervals. Presence of laminated clays in the upper Oligocene Chadra B and thick shale and siltstone interbeds in the lower Oligocene Diba Formation results in blocking the pay zone connectivity. Greatest pay zone thicknesses occur in Chadra B and Diba and the zones of best reservoir quality are those enriched in clean sand, non-tight limestone with minimal content of clay and highest ef-fective porosity and lowest water saturation. Dissolution pores are interpreted to be promi-nent in the Diba Formation and Chadra A, C.