A recent widespread realization that software experiments are not as easily replicated as once believed brought software execution preservation to the science spotlight. As a result, scientists, institutions, and funding agencies have recently been pushing for the development of methodologies and tools that preserve software artifacts. Despite current efforts, long term reproducibility still eludes us. In this paper, we present the requirements for software execution preservation and discuss how to improve long-term reproducibility in science. In particular, we discuss the reasons why preserving binaries and pre-built execution environments is not enough and why preserving the ability to replicate results is not the same as preserving software for reproducible science. Finally, we show how these requirements are supported by Occam, an open curation framework that fully preserves software and its dependencies from source to execution, promoting transparency, longevity, and re-use. Specifically, Occam provides the ability to automatically deploy workflows in a fully-functional environment that is able to not only run them, but make them easily replicable.