Underwater gas bubble expansion as a function of the ambient‐pressure to bubble‐pressure ratiop′, in the interval 0⩽p′⩽1, is investigated. At the endpoints, a simple analytic solution to the nonlinear equations of motion in closed form may be found; but, for intermediate values ofp′, an approximation is required. In the noncompressive case, representations suitable for large bubble radii, nearp′=0, and small‐amplitude motion, nearp′=1, are derived. A result of this analysis is that the Willis bubble pulse formula, correct in the limitp′ → 0, in agreement with experiment, appears to be valid over much of the interval, but it starts to break down asp′ → 1. The power law governing finite‐ and small‐amplitude periods is different; the actual period has no simple power law dependence, but may be deduced for allp′ by fitting a curve to the asymptotically correct values atp′=0 andp′=1, respectively. Owing to radiation and other loss mechanisms, bubble starting out as finite‐amplitude pulsation, with a cusplike shape at the minimum, is gradually transformed into a small‐amplitude damped sine wave; concurrentlyT1→T̄. (Analysis in this paper refers to caseγ = 43.)