Three sets of 10 MV x-ray zero-area phantom scatter correction factors have been obtained using three methods. The three methods are all based on the Bjärngard - Petti extrapolation principle. The three sets of data assume lateral CPE (charged particle equilibrium) for the primary absorbed dose. Using the most reliable set of data, a set of 10 MV x-ray SMRs (scatter - maximum ratios) is produced and parameterized. With respect to the zero-area correction factor at a depth of 2.5 cm, the parameterized expression gives and a Rice - Chin Monte Carlo simulation gives . The former is only 0.4% larger than the latter.