The term “marginal oil resource” refers to an oil reservoir that has hydrocarbon resource preservation but cannot meet the criteria of resources under the U.S Securities and Exchange Commission (SEC) standards. When oilfields step into their late life, most of their economic petroleum reserves have been well developed, and their focuses need to be switched to their intact marginal resources. In this paper, reservoir characteristics and key petrophysical properties of marginal oil resources are introduced to classify marginal oil resources into four types for identifying potential development opportunities. Primary recovery and its following development strategy are applied to fully utilizing their economic returns. Waterflooding, low salinity waterflooding (LSW) and enhanced oil recovery processes are reviewed to illustrate its potential uplift on oil production and application challenges such as higher clay content in marginal resources than in commercial reservoirs. An oilfield is presented as a case study to demonstrate the classification of marginal resources and illustrate successful economic development including learnings and challenges. This paper highlights the development potential of marginal resources and proposes a clear guidance for policy makers on how to tailor a development strategy supporting their economic development. This review could increase certainty on forecasting performance of marginal resources.