black gold 
noun [mass noun] North American informal
Oil.Palm oil production, fish, and now black gold and natural gas are major resources, as is education....
- The next big attack came in 1991, when they destroyed the country's capacity to export black gold - ‘oil, that is’ - to Tokyo.
- It is worth noting that the shelf of the Arctic seas washing the Russian coast concentrates up to 80 percent of all of the country's oil reserves, which is five times the reserves of black gold on the Arabian Peninsula.