There are three principles that must be followed in the design of oil wells: safety, productivity and environmental protection. Throughout the well s life there must be equipments that allow the operations to be carried out safely. The integrity of an oil well is critical to ensure such safety. Safety barrier elements are the basis of integrity management and therefore need to be suitable and work properly. Integrity is the containment of the well fluids, preventing hydrocarbons spills to the environment and between producing zones. The oil industry has faced several accidents throughout its history (eg Montara s field, Macondo s field, Frade s field) and such tragic events demonstrate the hazardous potential that the Oil and Gas industry may have. Millions of dollars are lost each year due to inefficient maintenance and unscheduled well shut-ins. Costs are very high, but possible threats to the environment and hazards to human life should be the top priority. This is why there is a growing concern and focus on the well s integrity. This work presents a methodology to verify the reliability of a barrier system in oil wells, providing a method able to compare different configurations of subsea wells, through simulations, using Monte Carlo Method. In order to verify the importance of some of these barrier elements in the system, some studies were conducted varying the failure rates of the studied element in question, leaving the other rates unchanged. In the end, a comparison of these results was made, observing which ones need to be even more reliable.