This article examines various methods to enhance the thermal efficiency of parabolic trough solar collectors (PTCs), both theoretically and experimentally. These methods include increasing the surface area of the absorber tube to increase its ability to absorb solar energy, placing a tube inserts inside the tube to induce turbulence and hence improve heat transfer. Among other methods are also minimization of reflection by using selective coatings on the surface of the absorber tube. Additionally, increasing the thermal conductivity of the working fluid, or modifying or altering the shape of the absorber tube or the reflective surface have also been shown to have improved thermal performance by minimizing energy losses due to conduction, convection, and radiation. All these and similar approaches that address and improve system parameters lead to improved efficiency and thermal performance, but they also entail a pressure drop and increase the cost of the system. In this study, the techniques that are used to improve the thermal efficiency of PTCs are addressed and presented in detail along with the findings of previous studies.