Single-shot methods suitable for determining capillary pressure and relative permeability curves are proposed. For steady-state gas flow, with stationary water or oil remaining in a porous rock core and the outflow boundary condition (capillary pressure is zero) is maintained by washing the outlet face of the core with the stationary phase, the gas pressure distribution, P(x), is determined by SPRITE (Single-Point Ramped Imaging with T.sub.1 Enhancement) MRI (Magnetic Resonance Imaging) spin density imaging of flowing gas, since the spin density of gas is directly proportional to the pressure of the gas phase. Water or oil saturation distribution, S(x), at the present of steady-state flowing gas, is measured with MRI. The combination of P(x) and S(x) yields a capillary pressure curve, P.sub.c(S) and relative permeability curve of flowing gas phase, K.sub.rg(S) can be determined with differential form of Darcy's law and ideal gas equations for gas flowing at steady-state. Some embodiments include the steps of providing a porous rock core having a length, an inlet face, and an outlet face; saturating the porous rock core with a first fluid; displacing the first fluid by applying a second fluid to the inlet face of the porous rock core; washing the outlet face of the porous rock core with said second fluid so as to maintain an outflow boundary condition; determining that a substantially steady-state condition has been reached whereat the fluid saturation distribution and pressure distribution along the length of the core do not substantially change with time; performing a single-shot measurement of at least one of a fluid saturation distribution measurement of the porous rock core and a pressure distribution measurement of the porous rock core; and determining a property of the porous rock core by using the single-shot measurement.