A concrete gravity dam is considered with typical dimensions and factors of safety against sliding were compared for conventional PFOS (IS 6512) and proposed PFOS. It is found that conventional PFOS recommends the revision of the design only for C/R interface at right bank. Whereas, proposed PFOS recommends the revision of the design for C/R interface at both the banks beyond a certain CL. The conventional PFOS (IS 6512) accounts only for environmental uncertainties while the proposed PFOS accounts only for strength criteria related errors. Proposed PFOS does not replace conventional PFOS. Both PFOS are complimentary to each other and hence, it is recommended that a better preliminary design must satisfy conventional as well as proposed factor of safety against sliding.