Biodiesel is great, right? Cooking oil that was going to be thrown away anyway gets converted to fuel that can be used in lieu of petrochemicals. When demand rises you turn surplus corn and soybean crops into biodiesel. Unfortunately, palm oil (often produced on plantations where rain forests once stood) is a cheaper source of biodiesel than recycled oils or anything we can grow in America, so an eco-friendly fuel turns into another threat for endangered ecosystems. We live in a complicated world.