In this article, the use of gas as a working fluid in the parabolic trough receiver (PTR) has been investigated numerically. The present study aims to determine which gas will work best as a heat transfer fluid (HTF) by analyzing the impact of several gases on the PTR’s performance. So, gases, such as carbon dioxide, helium, nitrogen, oxygen, hydrogen, methane, neon, and air, are considered in the present study, which flow through a thick-wall stainless steel pipe under a laminar flow regime. The temperature-dependent thermo-physical properties of the gas are considered. The finite difference method (FDM) with the harmonic mean technique is employed to solve this conjugate heat transfer problem. The current research findings are verified with those reported in the literature and are in excellent agreement. The grid-independent study is conducted to choose the optimal grid size. After that, the multi-objective function optimization technique and performance enhancement factor (PEF) is used to select the best suitable HTF, and it found that hydrogen gas is most appropriate based on these two criteria. Then, the influence of various parametric studies such as Reynolds number, solar flux, and receiver pipe thickness on the Nusselt number has been carried out. It is found that the Nusselt number increases with the Reynolds number while it decreases with solar flux and receiver pipe thickness. The significance of the current study may aid in choosing the appropriate gas as HTF in the parabolic trough solar collector (PTSC).