A simple equation has been developed for estimating the solubility parameters of live reservoir fluids at elevated pressure and reservoir temperature. The solubility parameters of live reservoir fluids have been simply related to their measured densities by a linear function. The equation has been validated using 45 reservoir fluids covering heavy oil, black oil, volatile oil, and gas condensate with a total of 760 data points. The gas to oil ratio (GOR) range is from (25 to 9369) m(3).m(-3), and the American Petroleum Institute (API) gravity varies from (16.6 to 50.2). The pressure ranges from (0.1 to 150.7) MPa, and the reservoir temperature is over a range of (323.9 to 422.0) K. The average absolute deviation of solubility parameters is 0.19 MPa(0.5) between the new equation and the method proposed by Wang et al. Furthermore, the new equation and the Peng-Robinson equation of state (PR EoS) have been used to calculate solubility parameters, and the results have been compared with the experimental data at pressures up to 30 MPa and 303.15 K for four pure hydrocarbons as well as dead and live oils. The predictions by the new equation and the PR EoS with an average deviation of < 0.5 MPa(0.5) are within the experimental uncertainty of < 0.8 MPa(0.5). The results show that the developed equation in this work can be successfully used to approximate the solubility parameters of live reservoir fluids in terms of their measured densities with good accuracy.