observation well occurrences of mineral and fossil fuels ocean energy ocean temperature gradient power station ocean thermal energy conversion ocean thermal gradient octane number odorisation odorising odorization odorizing offshore drilling offshore drilling platform ohm oil coke oil geology oil leakage sump oil pipeline oil pollution oil refining oil shale oil string oil tanker once-through boiler opencast opencast development open cast mining

open-cut development opencut mining opening up an opencast mine open mining open-pit development open-pit mining openpit mining open-type substation open-wire line operating capacity operating flow of a turbine operating range operating time operating voltage operational earthing operational grounding operation with earth return operation with metallic return operation with sea return optimum ambient wind speed optimum capacity optimum load orebody ore content meter ore deposit Organisation of Arab Petroleum Exporting Countries Organisation of Petroleum Exporting Countries

Organization of Arab Petroleum Exporting Countries Organization of Petroleum Exporting Countries outdoor substation outdoor switching compound outdoor switchyard outgoing feeder outlet output capacity overall consumption overall energy balance overburden overburden overburden ratio overflow overhead cable overhead conductor overhead earth wire overhead line overhead network overhead system overload capacity oversize overspeed device overvoltage own-production