A methodology for direct and simultaneous determination of four phenolic antioxidants-butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), propyl gallate (PG), and tert-butylhydroquinone (TBHQ)-in biodiesel samples using differential pulse voltammetry associated with partial least squares (PLS) regression is presented. Measurements were taken directly in a biodiesel:ethanol 1:1 (v/v) medium using a platinum ultramicroelectrode as the working electrode. The voltammetric signals of the compounds overlapped significantly, and to facilitate the simultaneous determination of the analytes, a PLS chemometric tool was applied and approaches fitting one compound at a time (PLS-1) and multiple compounds (PLS-2) both allowed the quantification of the individual concentrations, overcoming the strongly overlapped voltammograms. Results show that the PLS-2 model provides more accurate predictions than PLS-1. For the PLS-2 model, root mean square errors of prediction of 3 X 10, 16, 24, and 3 X 10 mg L-1 have been obtained between nominal and predicted concentrations for BHA, BHT, PG, and TBHQ, respectively. Recovery percentages were between 83 and 104%.