Precision measurements of positron lifetimes in aluminum at 42 temperatures are presented. The data are analyzed in a manner consistent with both trapping and nontrapping models of positron–vacancy interaction. Both models can be characterized by two parameters, the vacancy formation energy and a trapping or enhancement parameter. The two-component trapping model seems to be favored by the data, but a one-component interpretation is possible. The values obtained for the vacancy formation energy in aluminum are 0.71 eV according to the trapping model and 0.78 eV according to the nontrapping model.