The sterile insect technique (SIT) is currently the only available technology capable of eradicating the Old World screwworm fly (SWF) Chrysomya bezziana Villeneuve in the event of it invading Australia and successfully establishing itself. This is based on the success of of SIT in eradicating the New World screwworm fly, Cochliomyia hominivorax Coquerel in North America and Libya, North Africa and the demonstrated adaptation of SIT for the eradication of Chrysomya bezziana by Australian researchers in field trials in Papua New Guinea. The economic evaluation of the eradication of the Old World screwworm fly based on SIT in the event of an invasion of Australia is undertaken with a dynamic spatial bio-economic model using livestock data provided by the Australian Bureau of Statistics 1991 agricultural census. Direct producer losses for the beef cattle, sheep and diary cattle industries are used to establish the economic feasibility of several SIT eradication scenarios involving five factory sizes and ten entry points across Australia. The economic analysis is extended to include the use of economic surplus changes to measure the benefits and costs of eradication incorporating both producer and consumer welfare effects. The results indicate that in the event of an established invasion, the optimal size of a SIT factory appears to be one with a production capacity in the range of 200 to 250 million flies per week. Based on long-term average climate and vegetation and a worst-case scenario of the fly entering Australia through Brisbane at the beginning of the summer, the benefit-cost ratio (BCR) of the base eradication scenario involving a factory size of 250 million flies per week is 7.5. This BCR is based on the use of total direct producer losses to measure the benefits and costs of SWF eradication. The corresponding BCR is about 80% higher (13.9) when both producer and consumer effects are considered.