This paper describes the development and benchmarking of two ‘automobile fuel tank evaporation control system’ leak detection methods, which include 1) Positive pressure decay and 2) Negative pressure decay. In the past, negative pressure decay was the least expensive method that met the current OBDII requirement for a 1.0mm leak but these systems exhibit deficiencies when attempting a 0.5mm leak test. Positive pressure systems overcome most of these deficiencies but respond too slowly for evaporative control strategies of the future. Testing was done to compare the ability of each system to detect a 0.5mm fuel tank leak under various environmental conditions. It was found that both systems exhibit similar leak detection capability if a specific degree of stability is attained with respect to tank pressure.