The relationship of pressure and composition in the Henry's law regime has been experimentally measured in an equilibrium static cell for a set of binary organic-water mixtures. The solutes range from hydrophilic materials, such as alcohol to extremely hydrophobic components, such as toluene and 1,2-dichloroethane. The goal of this study is to determine the effective concentration range over which Henry's law reasonably approximates the gas-liquid partitioning. With the goal of obtaining accurate values of Henry's law constant, several methodologies are critically compared for the aqueous solutes examined experimentally. The apparatus employed can determine gas-liquid partitioning coefficients through a variety of methods including direct phase concentration ratios, equilibrium partitioning in closed systems (EPICS), and application of the coexistence equation for gamma (infinity). Results to date indicate a more complex dP/dx behavior in the dilute region than previously assumed; and Henry's law constant may not strictly apply to hydrophobic materials until the solute concentration is so low that analytical detection is problematic.