The PEA (Preliminary Environmental Assessment) at Petrobras consists, in general terms, of an internal technical process, prior to the environmental license, prepared to verify the environmental feasibility of a project, identifying the main environmental issues, as well as supporting development of the EIA (Environmental Impact Assessment Study). The technical guidelines for the PEA are prepared by the Environmental Assessment Engineering Team of PETROBRAS/ENGENHARIA/IETEG/ETEG/EAMB and are based on the characteristics of the project. The PEA is one of the elements of the environmental impact assessment, providing an initial assessment of the environmental aspects of the project (Screening). It also supports the assessment and determination of route and location alternatives of pipelines and industrial plants. The onshore phase of the Mexilhão Project consists of the construction of both the Caraguatatuba Gas Treatment Plant (UTGCA) that will process gas and condensate from Mexilhão Field, in the Santos Basin – SP, and the Caraguatatuba – Taubaté Gas Pipeline (GASTAU), between Caraguatatuba and Taubaté. The GASTAU will cross the Serra do Mar and connect the UTGCA to the Brazilian pipeline network, delivering gas. This study presents the procedures and conclusions of the PEA prepared for the UTGCA and GASTAU projects by PETROBRAS/ENGENHARIA/IETEG/ETEG/EAMB.