When it comes to non-standard natural gas and natural gas resources, you might immediately think of coal and shale gas. But there is another type of lower-level energy, accounting for over 15% of the world's unconventional oil and gas resources, and that is oil sands, a "restricted" energy source. 
Oil sands, also known as "tar sands" or "bitumen sands", are mainly composed of asphalt, sandy materials rich in mineral clay, and water containing approximately 6 - 12% asphalt. 80 - 90% of the minerals such as sand and clay, and the remaining 3 - 5% is water. Oil sands possess the production characteristics of solid mineral deposits and the source characteristics of petroleum residues.