Synthetic biology has been presented as the application of engineering principles to (genomic) biology. But in industrial synthetic biology, alongside the much discussed engineering principles of abstraction, modularity, de-coupling and standardisation, we see many other practices of contextualisation through which engineering projects accrue credibility and realisability. This paper discusses how synthetic biologists working on next-generation biofuels construct an economic calculus for biological forms. As they modify microbes to make fuel from plants, waste gases and sunlight, or introduce new metabolic pathways into organisms, they also create novel stories that link economic and metabolic processes, and they attach new contexts to synthetic biology in various forms ranging from global climate change, peak oil, food security, US foreign policy, through to fashion and diet. Examples drawn from well-known next-generation biofuels companies such as Joule Unlimited, Amyris Technologies, Synthetic Genomics, Solazyme and Aurora Algae illustrate how principles of cosmogonic dreaming, metabolic equivalence and supply chain disruption strain to connect the origins of life on earth, the flux of solar radiation, the optimal metabolic flux in a microbe and the prices of petroleum, palm oil or sugar. This economic calculus both connects engineering practice to a plurality of life forms, and creates a space in which synthetic biology can appear as unprecedented.