Studies have shown that methane production by ruminants may be able to be reduced by dietary change or rumen microbial modification. However, there is a growing need to provide an assessment of the viability of potential options for reducing the emissions of both methane (CH4) and nitrous oxide (N2O) from agricultural sources. In this study, the potential for reducing emissions of CH4 and N2O from agricultural sources and the likely costs associated with each option will be investigated. Results will be provided in the form of marginal and total cost curve analyses for each gas with respect to national impact, different agricultural sectors and typical management systems. The study will be composed of 4 specific objectives outlined as follows, together with ways in which they might be achieved: 1. To review potential methods for reducing N2O emissions from agriculture and assess the consequences and needs for management practices. A means of defining and calibrating the potential for achieving abatements will be established where there is inadequate experimental data. The costs associated with each method will be estimated and the likely impact on N2O that proposed measures for reducing NH3 emissions may have will be evaluated. Methods being developed for UK agriculture inventory of N2O will also be examined; 2. To review potential methods for reducing CH4 emissions from ruminants, to assess the potential for reducing CH4 emissions from other components of animal production systems, and to quantify the impact that CH4 exchange with soils may have. Costs associated with reduction of CH4 emissions will be estimated and the importance of other contributing sources to net UK CH4 emissions will be determined. Effects of deposition, management, storage and application of excreta will also be investigated; 3. To examine and develop/modify the existing model structure developed by ICCET for cost curve analysis for NH3 abatement or, if necessary, develop alternative approaches for cost curve analysis of CH4 and N2O based on individual emission factors. The final model will be used to calculate altered emissions after implementation of mitigation measures (dependent on efficiency and applicability). This will allow construction of cost curves and calculation of unit costs for each method. Marginal and total cost curves will be constructed, the latter of which will provide the cumulative cost of mitigation to a particular level; and 4. To produce model outputs to define the relative effectiveness of available and proposed methods for reducing CH4 and N2O emissions in relation to estimated costs using a cost curve analysis for UK agriculture and its component sectors. Marginal and total cost curve analyses for the 2 gases will be performed using a range of different scales and scenarios, i.e. total national impact, different agricultural sectors at a national level and a range of typical management systems.