Inconel 718 is a hard-to-machine nickel-based alloy used for aerospace component manufacturing. The machining of Inconel 718 causes severe tool failure due to the heat generated by high friction forces. Therefore, cutting tool performance can be optimized by using a suitable cutting fluid. This paper compares the effects of synthetic and oil-based cutting fluids on wear mechanisms and failure modes of the PVD-TiAlN/NbN coated inserts during face milling of Inconel 718. Face milling was conducted by varying cutting speed at constant feed rate, axial and radial depth of cut. Flank wear (VB) was measured before the inserts were examined in SEM and EDX for tool wear mechanisms characterisation. Chipping, built-up edge (BUE) and severe notching were the most dominant failure modes observed in all cutting conditions. Pitting, galling and coat delamination associated with chipping and minor BUE were observed at low cutting speed. At high speed, progressive nose notching was the main cause of tool failure. At low cutting speed, dry cutting produced the longest tool life followed by oil-based and synthetic cutting fluids. At higher cutting speed, synthetic fluid had the longest tool life followed by oil-based cutting fluid and dry cutting. This research provides an insight on the influence of cutting speed to the choice of cutting fluids during machining so that tool wear can be minimized.