The main concern of activities developed in oil and gas well construction is safety. But safety during the well construction process is not a trivial subject. Today risk evaluation approaches are based in static analyses of existent systems. In other words, those approaches do not allow a dynamic analysis that evaluates the risk for each alteration of the context. This paper proposes the use of Quantitative and Dynamic Risk Assessment (QDRA) to assess the degree of safety of each planned job. The QDRA can be understood as a "safe job analysis" approach, developed with the purpose of quantifying the safety degree in entire well construction and maintenance activities. The QDRA is intended to be used in the planning stages of well construction and maintenance, where the effects of hazard on job sequence are important unknowns. This paper also presents definitions of "barrier", and "barriers integrated set" (BIS), and a modeling technique showing their relationships. (c) 2006 Elsevier B.V. All rights reserved.5141671111126