Seismic fragility analysis was performed for API X65, a type of buried gas pipeline that is widely used in Korea. For this purpose, nonlinear time-history analyses were carried out using 15 different analytical models of the pipeline, which represent variations of modeling parameters. The nonlinear Winkler approach was adopted to simulate the soil-pipeline interaction during an earthquake loading. A set of 12 recorded ground motions were selected for the time-history analyses and scaled to represent a range of earthquake intensity levels. Then, fragility functions were developed with respect to the damage states, which are defined in terms of the maximum axial strain of the pipeline. The parameters under consideration for subsequent seismic fragility analyses are the soil conditions, boundary conditions, burial depth, and type of pipeline. Comparative analyses revealed that the first three parameters, most notably the soil conditions, influence the fragility curves, but the last parameter negligibly affects the fragility curves. It is concluded in short that this study is promising to give a useful insight for a rapid seismic performance evaluation of a buried gas pipeline based on nonlinear and fragility analyses.