Microemulsions (µE) were prepared with palm fatty acid methyl esters (PFAME) as solvents, and stabilized by ethoxylated non-ionic surfactants, i.e., Dehydol LS 7 and Dehydol LS 2 as S_A and S_B with the hydrophiliclipophilic balance (HLB) values at ~12.8 and ~7.3, respectively. The co-surfactants chosen were 1,2-hexanediol, 1,2-butanediol, 1,2-ethanediol and glycerol. The effects of the co-surfactants on the partial ternary phase diagrams were studied at 10%, 15%, 20%, 25%, 30% and 40% (w/w) concentrations. The ratio of PFAME to water was either 25:75 or 50:50. The mixtures were agitated vigorously, and then kept at ambient temperature (25°C) for one to two days. The emulsions (two-phase), the µE and liquid crystalline phases were observed using polarised light. In addition, the physical stability of the µE solutions was determined at 45°C over a period of one month. The effects of the co-surfactants on the ternary phase systems for PFAME/non-ionic surfactants/water were studied and mapped out at 25°C and 45°C, respectively.