<P> In 1947 an even bigger field opened at Leduc, 20 miles (32 km) south of Edmonton, and in 1948 oil mining began at Redwater . Both these fields were overshadowed in importance in 1956 with the discovery of the Pembina field west of Edmonton . Other fields were discovered east of Grande Prairie and in central Alberta . From collection and distribution points near Edmonton the oil is sent by pipeline to refineries, some as distant as Sarnia, Toronto and Montreal to the east, Vancouver to the west, and especially the U.S. to the South . Interprovincial Pipe Line (IPL) began in 1949, transporting oil to refineries in the east . IPL became Enbridge Pipelines in 1998 and now has 4500 employees; it moves 2 million barrels a day over 13,500 miles of pipe . </P> <P> Alberta produced 81% of Canada's crude oil in 1991, when Alberta's traditional oil fields peaked; output is now steadily declining . Before the 1970s, the major producers were controlled by U.S. oil giants . </P> <P> Exploration for oil led to the discovery of large reserves of natural gas . The most important gas fields are at Pincher Creek in the southeast, at Medicine Hat, and in the northwest . TransCanada pipeline, completed in 1958, carries some of the gas eastward to Ontario and Quebec; other pipelines run to California . Alberta produces 81% of Canada's natural gas . An early pioneer in the discovery and use of natural gas was Georg Naumann . </P> <P> The "oil sands" or "tar sands" in the Athabasca River valley to the north of Fort McMurray contain an enormous amount of oil, one of the world's richest deposits--second only to Saudi Arabia . The first plant for extracting oil from the tar sands was completed in 1967, and a second plant was completed in 1978 . In 1991 the plants produced about 100 million barrels of oil . Expansion was rapid, with very high paid workers flown in from eastern Canada, especially the depressed Maritimes and Newfoundland . In 2006 bitumen production averaged 1.25 million barrels per day (200,000 m / d) through 81 oil sands projects, representing 47% of total Canadian oil output . The processing of bitumen, however, releases large amounts of carbon dioxide, which has alarmed environmentalists worried about global warming and Canada's carbon footprint . </P>

When did european exploration of the area known as alberta begin