This study was aimed at understanding how the interfacial tension (IFT) between novel ethoxylated cationic gemini surfactants and oil is affected by various spacer types. These surfactants possess similar hydrophobic tails, ethoxy units, and head groups, and the effect of the nature of the spacer on the IFT was exclusively studied. These surfactants were mainly classified into three different groups to examine the effect of spacer length, unsaturation, and aromaticity. The spacers of the first group of the surfactants were composed of different numbers of methylene units (4, 6, 8, 10, and 12). The second group consists of three surfactants where the spacers have saturation, unsaturation with a double bond, and unsaturation with a triple bond. The surfactants of the third group consist of four surfactants that have mono- and biphenyl rings in the spacer, in addition to different counterions. The experiments were performed at different surfactant concentrations and at different NaCI concentrations. The model oils used were n-decane and n-hexadecane. Increasing the spacer length from 4 to 10 reduced the IFT of the water/oil system irrespective of surfactant concentration, salinity, and oil type. A further increase in the spacer length from 10 to 12 increased the IFT. Moreover, both surfactants with a single bond and a double bond in their spacers did not have significant differences in IFT values. However, the surfactant with a triple bond spacer exhibited considerably lower IFT than the surfactant with a single or double bond spacer. The rigidity induced by the unsaturation of the spacer was the main reason for varying IFT values. Surfactants containing two phenyl rings in the spacer showed lower IFT compared to the surfactant-containing single phenyl rings. Moreover, chloride counterions on the phenyl rings accentuate the decrease in IFT when compared to bromide ions due to the ease of chloride ions associating with water molecules. This study showed that for a similar tail and head, spacer characteristics can have a substantial impact on the IFT. Moreover, it can help in understanding how to choose optimal spacers for IFT reduction.