The diligent use of capital of all forms contributes to sustainability. In fact, capital employment is a common factor in sustainability research and in the practice of sustainability management.  For example, capital usage is included in research in environmental sustainability in the context of sustainable consumption. Product/Service Systems (PSS), which includes product sharing as one concrete form, has been addressed in research on that context. However, virtually no literature provides concrete, theory-based methods for quantifying the effects of sharing products. The goal of this paper is to describe the potential contribution of portfolio theory in order to quantify the effects and optimize the employment of capital in a theoretical and quantitative manner in the context of sustainability. Practices tied to the prescriptions of portfolio theory can contribute to environmental sustainability. The core perspective can be summarized as follows: the pooled, portfolio approach to asset management yields a reduction in assets employed and used relative to the volume of demanded resources used for need fulfillment.

To reach this goal, the paper first provides a brief literature review from the “finance side” of literature. Then, the “engineering side” literature offers a few examples of others who have applied the prescriptions of portfolio theory to “engineering” application.

After that, it provides an overview of the core issues and implications of portfolio theory, and develops some ideas to support application of portfolio theory. The provided insights illustrate how portfolio principles applied outside the arena of investments can yield benefits, including the fulfillment of needs with the least resource used – a core principle in sustainability. In particular, the “pooling” of assets/services to meet uncertain demands from different users of an asset/service pool may yield benefit from diversification effects.

Furthermore, the paper offers additional avenues for future research. It describes how this special application of portfolio theory outside the realm of finance can yield benefits that positively affect the creation of value and resource use in an economy at large.