Ejector refrigeration system (ERS) is a favourable technology to recover the available exhaust heat of automobiles for cooling purposes due to its uncomplicated structure, low cost and easy maintenance compared to the other systems. Despite these advantages, it suffers from poor performance because of the irreversible fluid flow structures inside the ejector. The refrigerant variant used, operating parameters and design specifications influencing the ejector flow can affect the ERS performance significantly. As per the European Parliament Directive 517/2014, the restrictions towards the usage of high global warming potential (GWP) refrigerant R134a reveals the necessity to find low-GWP alternates. Accordingly, in the present study, a real gas property-based theoretical model is developed to estimate the ERS behaviour with six low-GWP substitutes for R134a: R1234yf, R1243zf R1234ze(E), R152a, R513a and R440a. Within a wide variety of evaporator and generator temperatures, the performance of the proposed model is analyzed under the critical mode of operation. Results indicate that for R1243zf and R1234yf ejector cycles, the entrainment ratio is maximum and almost equal. The coefficient of performance is observed as maximum and nearly equal with R152a and R440a. Though the COP values are higher for the refrigerants R152a and R440a because of their higher GWP, it is suggested to use the next higher COP refrigerants R1234yf and R1243zf in the ERS integrated with automotive applications.