A new form of equation of state is proposed for use over extremely wide ranges of pressure where conventional equations fail. In particular, fluids including H2O and CO2 as well as argon, etc., remain more compressible at very high densities than can be represented by typical equations with van der Waals or Carnahan and Starling repulsive terms. The new equation is fitted to the data for H2O and CO2 over the entire range from the vapor and Liquid below the critical temperature to at least 2000 K and from zero pressure to more than 10(5) bar (10 GPa) with good agreement. The extension of the equation for mixed fluids is discussed.