A conventional method to estimate the damping of an oscillatory system is the execution of amplitude extinction tests. In the specific case of the roll motion of a vessel, the so-called roll decay tests are performed in a model basin. During these tests, the system is posed in an imbalance condition by an external moment. For systems where the damping is far below critical value, the transient decay to equilibrium condition is oscillatory. There are several methodologies to analyze the decay test time-series, all based on the assumption that a pure roll motion has been reproduced. Through this paper an overview of the most commonly used methods is given and a comparison of the results is shown for a single ship model decay test.