Two-component mass models, consisting of an exponential disk and a spherical halo, are constructed to fit a newly determined rotation curve of NGC 3198 that extends to 11 disk scale lengths. The amount of dark matter inside the last point of the rotation curve, at 30 kpc, is at least 4 times larger than the amount of visible matter, with M/L(B)tot = 18 solar M/L(B). The maximum mass-to-light ratio for the disk is M/L(B) = 3.6. The available data cannot discriminate between disk models with low M/L and high M/L, but arguments are presented which suggest that the true mass-to-light ratio of the disk is close to the maximum computed value. The core radius of the distribution of dark matter is found to satisfy R(core) of between 1.7 and 12.5 kpc. 31 references.