Petroleum hydrocarbon pollution in soils/sediments is a primary concern in ecosystems and occurs as a result of human activity, causing instability in growth and development. Bioremediation is a biotechnological strategy using plants, bacteria, and fungi to stabilize, control, remediate, and restore the environment. Principle treatment targets are soils and sediments polluted by petroleum contaminants. Co-composting technology, an ex-situ bioremediation method, has gained attention for its high-efficiency removal of petroleum-hydrocarbon-based contaminants in soil and sediments. Bulking agents are co-composting amendments and enhancers of bioremediation that are used to create inter-particle voids, providing air space in composting materials, and regulating the water content of waste. In this chapter, different aspects of a suitable bulking agent for co-composting petroleum hydrocarbon-contaminated soils/sediments, and a case study regarding the use of sugarcane bagasse in co-composting are reviewed and dissected.