Olive oil industry is one of the most important industries in the world. Currently, the land devoted to olive-tree cultivation around the world is ca. 11 × 10⁶ ha, which produces more than 20 × 10⁶ t olives per year. Most of these olives are destined to the production of olive oils. The main by-products of the olive oil industry are olive-pruning debris, olive stones and different pomaces. In cultures with traditional and intensive typologies, one single ha of olive grove annually generates more than 5 t of these by-products. The disposal of these by-products in the field can led to environmental problems. Notwithstanding, these by-products (biomasses) have a huge potential as source of energy. The objective of this paper is to comprehensively review the latest advances focused on energy production from olive-pruning debris, olive stones and pomaces, including processes such as combustion, gasification and pyrolysis, and the production of biofuels such as bioethanol and biodiesel. Future research efforts required for biofuel production are also discussed. The future of the olive oil industry must move towards a greater interrelation between olive oil production, conservation of the environment and energy generation.

Bio-oil is a promising source of chemicals and renewable fuels. As the liquid phase obtained from the pyrolysis of biomass, the composition and amount of bio-oil generated depend not only on the type of the biomass but also on the conditions under which pyrolysis is performed. Most fossil fuels can be replaced by bio-oil-derived products. Thus, bio-oil can be used directly or co-fed along with fossil fuels in boilers, transformed into fuel for car engines by hydrodeoxygenation or even used as a more suitable source for H₂ production than biomass. On the other hand, due to its rich composition in compounds resulting from the pyrolysis of cellulose, hemicellulose and lignin, bio-oil co-acts as a source of various value-added chemicals such as aromatic compounds. This review presents an overview of the potential applications of bio-oils and the pyrolysis conditions under which they are obtained. Then, different extraction methods for value-added chemicals, along with the most recent developments, are discussed and future research directions for bio-oil upgrades are highlighted.