Both experimental oil release field studies, in Arctic tundra, freshwater, and marine ecosystems, and follow-up studies after Arctic and subarctic oil spillages indicate long persistence times for hydrocarbon contaminants and slow rates of microbial biodegradation. The slow rates of petroleum biodegradation in Arctic ecosystems are not due to a lack of indigenous hydrocarbon-degrading microorganisms since virtually all Arctic ecosystems contain numbers of naturally occurring populations of hydrocarbon-degrading microorganisms, and generally numbers of hydrocarbon degraders increase following addition of oil. Low temperatures alone also can not explain the limited rates of hydrocarbon biodegradation. Rather the limitation to microbial degradation of petroleum hydrocarbons in Arctic ecosystems appears to be due to the combination of several factors, including the availability of nitrogen, phosphorus, and oxygen. Although the potential for hydrocarbon degradation exists, the actual rates of hydrocarbon biodegradation in Arctic ecosystems are slow; microbial hydrocarbon degradation can decontaminate Arctic ecosystems but the time frame after a major spillage will be decades rather than years.