multi-enterprise integration projects are unbearably costly for many companies. With a view to realizing lower integration costs and resources, enterprises are seeking partner attributes that display the ease of B2B collaboration. This paper examines the relationship of B2B interoperability to integration effort. It breaks down enterprise interoperability into five layers (network, data, process, application, business) and investigates the particularity and effect of each. The research model is validated by a field study using data from 239 firms. Interoperability at the business, process, and data levels is found to be significantly but negatively associated with integration efforts. Interoperability at the application level showed little relation to integration efforts, and interoperability at the network level had a nonsignificant positive relationship with integration efforts. The research model and findings are a starting point for assessing interoperability with a potential partner at each layer and for estimating the involved integration effort, with a view to aiding e-partnership decisions and B2B integration management.