The Mintabie Precious Stones Field (MPSF) has, since the early 1920s, produced some of the finest quality opal in the world. This report provides a review for understanding the remaining opal resources likely to exist there. A detailed spatial analysis conducted in 2018 showed that after approximately 40 years of mining in the MPSF, an area totalling less than 2 square km has been intensively mined. A conservative estimate of the area of greatest prospectivity within the MPSF is 20 square km. Within this region of high prospectivity, assuming a similar deposit density to the intensively mined areas to date, the MPSF will support mining for ~400 years at the levels already experienced in its lifetime. A complementary prospectivity analysis based on scout drillhole stratigraphic data, which was published in 2002, revealed that there are other arguably prospective but as yet unmined regions within the MPSF totalling 44 square km. Based on known indirect economic indicators, the total value of the (wholly unreported) amount of opal mined at Mintabie up to 2016 has been estimated by the South Australian Government to be $412M (unadjusted value of rough opal). An area-based analysis concludes that this is likely to be less than 10% of the total contained opal at Mintabie. The possible entire opal resource in the MPSF, including the opal already found, is therefore estimated to have an unadjusted raw opal value of over $4B. In the current edition of this report, reasons are given for the present decline in opal production at Mintabie, and recommendations are made for adopting new science-based opal prospecting methods which might increase the useful knowledge about the field's geology and controls on opal distribution, besides improving the chance of making new discoveries and boosting overall production.