Analytic results on the nonlinear evolution of the Rayleigh-Taylor instability into equatorial spread F bubbles are presented. The nonlinear saturation amplitude and k spectrum of he inertia-dominated Rayleigh-Taylor instability is computed in two dimensions (east-west and vertical). Analogous to the collisional case, the dominant nonlinearity is found to be two dimensional. The linearly most unstable modes which are primarily horizontal (kx<ky) saturate by nonlinear generation of vertical spatial harmonics which may be damped by either recomination or diffusion. The resulting 1/kx amplitude spectrum is consistent with observations and suggests that bubbles will be vertically elongated in the inertial as well as collisional regimes.