The design of O&G production facilities aims at high availability and low production cost by using different configuration such as series, parallel, K-out-N, stand-by, etc. Which is the best alternative? What are the relative gains and losses? This type of question happens in most regular technical meetings of O&G companies. There are many models developed in the literature, but with restricted application in real problems because authors look for mathematical properties that are seldom in accordance with real world problems. In this paper, we approach the problem using Monte Carlo simulation and spreadsheet with the following steps: (1) Reliability modeling of time-to-failure of equipment in active and stand-by function, (2) Statistical modeling on time to carry out maintenance, (3) Reliability and Availability modeling of the system with different configurations. After that, some alternative stand-by policies are studied such as: (a) keep asset in the same function, that is, in case of failure of an asset in the active function, it returns after preventive replacement or repair; (b) Carry out rotation of functions involving the standby and active asset in operation after each outage; (c) Rotate the standby and the active asset from time to time. The analysis of results of each of these policies over the system performance and total cost can be estimated using Monte Carlo simulation. The present work uses this model, resulting in the following conclusions: (a) as more redundancies are added, cost increases (capex, more equipment under maintenance, etc.), but the reliability of the system also improves and (b) with stand-by configuration it is possible to increase system's availability. However, it is important to analyze each case in order to find the optimal solution and there is no rule-of-the-thumb to solve all problems.