Mechanical properties of oil shales as a function of temperature and pressure are reviewed. Implications of evolution of these properties for in situ exploitation and basin modelling are explored. Mechanical properties at room temperature are well known. The existing data suggest a positive correlation between oil shale grade (organic matter content) and Poisson ratio, whereas tensile and compressive strength as well as modulus of elasticity show negative correlations. These properties are strongly affected by temperature. An increase in temperature results in loss of strength and decrease in Young's modulus. Strength follows a logarithmic decrease with increasing temperature, depending on grade. Creep is much enhanced by elevated temperature. Extrapolation of laboratory data to nature suggests that tensile fracturing may occur more easily during petroleum generation, and creep is more prominent in oil shales than in other rocks at this depth in the crust. More high-temperature experiments are required to validate these conclusions.