Problem, research strategy, and findings: It is commonly asserted that so-called compact development is the urban form most able to sustainably accommodate growth by reducing travel distances and conserving land, but credible supportive evidence remains limited. This study rigorously and realistically tested the relative performance of spatial options over the next 30 years for three distinct kinds of English city regions. Statistical models first forecast the behavior of people within interacting markets for land and transport. These outputs were then fed to established simulation models to generate 26 indicators measuring the economic efficiency, resource use, social impact, and environmental impact of the spatial options. This permitted an explicit comparison of the costs and benefits of compact against sprawling urban forms for these regions. While the prototypes (i.e., compaction, sprawl, edge expansion, and new towns) were indeed found to differ in their sustainability, no one form was clearly superior. Rather, the change to white collar lifestyles and associated population growth dominates the impacts on the natural environment and resources, far overwhelming those attributable to spatial urban form. Takeaway for practice: Urban form policies can have important impacts on local environmental quality, economy, crowding, and social equity, but their influence on energy consumption and land use is very modest; compact development should not automatically be associated with the preferred spatial growth strategy. Research support: The research was funded by the UK Engineering and Physical Science Research Council.