Unconventional fossil hydrocarbons fall into two categories: resource plays and conversion-sourced hydrocarbons. Resource plays involve the production of accumulations of solid, liquid or gaseous hydro-carbons that have been generated over geological time from organic matter in source rocks. The character of these hydrocarbons may have been modified subsequently, especially in the case of solids and extra-heavy liquids. These unconventional hydrocarbons therefore comprise accumulations of hydrocarbons that are trapped in an unconventional manner and/or whose economic exploitation requires complex and technically advanced production methods. This review focuses primarily on unconventional liquid hydro-carbons. The future potential of unconventional gas, especially shale gas, is also discussed, as it is revolutionizing the energy outlook in North America and elsewhere.

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Experience gained while modelling a petroleum geological database can be summarized as follows. General-purpose database models should reflect the real world, complete with imperfections, and avoid being application-oriented in design. In geological database modelling it is necessary to separate the recording of descriptive features (empirical data) from that of geological processes (concepts). Detailed analysis reveals that many geological relationships assumed to be inherently hierarchical are in fact many-to-many. Ambiguity and inconsistency in definitions should be avoided, if necessary by adopting a definition at variance with industry norms. Use of generic entities simplifies the modelling exercise and can benefit the end-user.

Over the past 75 years, hydrocarbon exploration of Arctic regions north of the Arctic Circle (668N) has yielded some 450 discoveries which collectively account for 2.5% of global conventional liquids discovered to date and 15.5% of the world's discovered conventional natural gas. Accumulations occur in rocks ranging from Cambrian to Pleistocene in age but 94% of all Arctic hydrocarbon resources occur in clastic reservoirs of Mesozoic age. Although discoveries have been reported from 15 different basins onshore and offshore Alaska, Canada, Norway and Russia, 75% of all discovered resources are located in the portion of Russia's Western Siberia Basin that lies north of 668N. Hydrocarbon accumulations discovered in the Arctic region have been generated from nearly 40 different petroleum systems. The main elements of these petroleum systems such as sources, reservoirs and seals are described and the chronology of these depositional events is summarized in two chronologic charts representing the Eastern and Western hemispheres.