The routing of the Trans-Anatolian Pipeline plays an important role in the future energy security of the European Union. The natural gas pipeline is planned to run from the natural gas fields in the Caspian Sea through Turkey. This project is a case study for a Geographic Information System (GIS) least-cost route analysis of a section of the proposed pipeline in Western Turkey. The route analysis comprised of weighting multiple types of criteria in a compiled risk assessment map that was analyzed by a least-cost algorithm to display the least hazardous route through the study area. Multiple varieties of criteria were considered such as, lithology, slope of terrain, environmental and social risk factors, e.g. proximity to natural reserves and urban centers, to provide the least hazardous route through the region. The derived least cost paths were more efficient than the proposed route in the relative cost associated with each route.