Conversion of oil feedstocks to fatty acid alkyl esters is a necessary step to produce biodiesel and other biobased products. These conversion processes must be robust for a number of different feedstocks containing varied oil profiles and contaminants. Furthermore, the final products may have specific compositional requirements to provide desirable properties for a particular application. In this work, conversion processes are used to modify fatty acid methyl ester (FAME) profiles from triacylglyceride (TG) feedstocks. A system using an acid heterogeneous catalyst with carbon dioxide as a reaction cosolvent is used to convert mixed TG feedstocks to FAME while illustrating resilience to reaction contaminants, such as water and free fatty acids (FFA). The presence of water does not show negative impacts on the reaction at loadings of up to 15 wt % (mass water/mass TG). Likewise, the presence of FFA does not negatively impact the reaction and in some cases improves TG conversion in the mixed system. Single FFA and TG reaction kinetics are evaluated across a range of alkyl chain lengths and degrees of unsaturation. FFA show faster kinetics compared to TG, while both feedstocks' conversions vary based on alkyl chain degree of unsaturation. Conversion of commercial vegetable oil feedstocks is evaluated illustrating that certain FAME formation is favored based on chain length and relative abundance. Overall, a FAME yield of 86% from palm oil was obtained in 4 h of reaction with methyl palmitate and methyl oleate yields dominating the produced FAME (87% and 95% yields, respectively). This selective conversion may be used to improve FAME product properties for select applications and should be considered in process design.