Using different methods of extraction guarantees that the highest concentrations of oils can be extracted. Essential oils are gathered from many different types of plants and many different parts of those plants. Flowers, fruits, herbs, stems, roots, leaves, buds, blossoms, seeds, nuts and even tree bark produce some of the most aromatic and therapeutic essential oils. Essential oil extraction methods fall under three main categories: expression, solvent extraction and distillation. The following is an overview of these extraction processes and methods. Read more about aromatherapy candles.