To protect components from abrasive wear, modern fuel systems require fine filtration. Many current fuel filter test standards such as SAE J905 and ISO 4020 use gravimetric analysis to determine filter efficiency. Gravimetric analysis can be ambiguous when differentiating between fine filters in terms of efficiency. Furthermore, it is impossible to determine the size rating of a filter using the gravimetric method. Optical particle counting as practiced in other test standards, such as SAE J1858, has proven to be a more useful method of determining filter efficiency. Not only is optical particle counting a precise method, but it also relates efficiency to specific particle sizes. This paper illustrates the feasibility of particle counting fuel filter bottle samples to determine fuel filter efficiency.In this study, test results determining efficiency derived from both gravimetric and particle count analysis are compared. The results show that filters with similar gravimetric efficiencies can have significantly different particle removal characteristics.