Scenarios of low permeability and long transient flow periods present in tight gas reservoirs, set out a major challenge on the reserves estimations. Consequently, these cause high uncertainties in volumetric estimates of gas (OGIP) and impacts in the deployment of technical and economic strategies in most projects. Flowing material balance equation and decline curve techniques in tight gas reservoirs, have serious drawbacks to predict the original gas in place (OGIP). However, both techniques combined yield better modeling results, as shown by Cox et. Al. The aim of the present research is to propose a method based on the Gas Production analysis (GPA) technique with the Palacio & Blasingame approximations in conjunction with pressure transient analysis for diagnostics specialized of Linear Flow, which improve the confidence in reserve estimations, specifically in early time production. The proposed method was applied in Lajas Formation of Neuquen Basin, Argentina, where a 20% maximum error decrease is expected in the OGIP, compared with non-type curve methods to the procedures (Hyperbolic and Exponencial model) in early time production. When permeability and porosity values are higher, the error of this methods increases. This is mainly due to the fact that infinite acting flow periods are shorter. However, in low permeability scenarios the OGIP estimation may achieve acceptable outcomes since infinite acting flow last longer.