During 1987, SADME reviewed the gas reserves of the Moomba Field (Morton & Scholefield, 1987). Following the completion of that report, significant differences between reserve figures prepared by Santos and SADME were highlighted. Differences were noted firstly in calculation methodology, and secondly, in the quantity of volumetric estimates. Since then, several meetings have been held with Santos during 1988/1989, in an attempt to resolve the differences, but no significant agreement has been reached. Additional field geological data has been gathered since 1987, including the from drilling of 7 wells and the initiation of a programme of special core analysis under a SADME / NERDDC / SENRAC / Santos - funded grant. As a consequence, it was deemed necessary that SADME's previous volumetric estimate for Moomba Field be reviewed. This has been done, and the 1989 volumentric review incorporates a new porosity equation based on the results of recent core analysis, including the effects of overburden pressure. Water saturation is now determined using a Waxman-Smits equation (instead of the Indonesion equation) in which clay content is derived from cation exchange capacity (instead of using the gamma ray log response). Porosity cutoffs are now a variable function of the gamma ray log response, using RFT permeability to delineate permeable from non-permeable reservoir. In Moomba North, restrictive drainage circles for proven and probable pay take account of the widely spaced wells and the variable nature of the reservoirs.