This paper derives lifetime distributions for components that fail due to overloading. We introduce the notion of energy similarity. This makes it possible to use knowledge about how components behave under different loads in order to establish a probability model. To obtain parametric families, we consider two physically distinct cases: (1) components that function individually and (2) components that function as part of a system. The former leads to univariate and the latter to multivariate models. The results are particularly useful when little or no data is available.