If agriculture is included in an Australian emissions trading scheme then it may face from 2015 at the earliest, a price for its greenhouse gas emissions; and thereby have incentives to offset and lessen its emissions. Yet because there is currently little understanding of the spatial pattern of emissions in agricultural regions of Australia, the extent of the challenge the sector faces in reducing its emissions is not fully recognised. To improve our understanding, this study uses the National Greenhouse Accounts methodology to estimate the spatial and temporal patterns of agricultural emissions since 1990 in the key agricultural region in Australia’s southwest. This region generates almost 40 percent of the nation’s winter crop production and supports over a quarter of the nation’s sheep. The quantity and trajectory of emissions from each shire in this region are reported, thereby identifying where emission problems may be worsening or easing. The composition and causes of changes in emissions are discussed. This study also generates spatial estimates of sequestration costs by drawing on land and forestry cost and tree growth data. Many relatively low cost sites for carbon sequestration, based on permanent reforestation, are identified with the implication that agriculture may be able to cost-effectively offset its emissions, as well as some of those from other sectors. However, an implication of this study’s findings is that in some shires eventually there may be strong land use competition between farming and forestry.