The contention that “most of the Alaskan Oil goes to Japan” has been around a long time. Was it ever true? Perhaps before the pipeline to Valdez was complete, or immediately thereafter?
No, and it started as a rumor before the oil was even produced. That is why it was illegal to export Alaskan North Slope Crude; it became necessary to get the legislation passed for the pipeline.
The ban against exporting Alaskan North Slope was lifted in 1996. Between 1996-1999 5.5% of North Slope oil was exported to Asian countries. These exports were overwhelmingly supported by the US Congress and by the Clinton Administration to offset an oil glut in California at the time. In June 2000 Alaskan North Slope oil again ceased to be exported, and 100% of Alaskan North Slope production has stayed in America.
More oil went to South Korea during this time than Japan. A little even went to China.
U.S. Crude Oil Exports to South Korea
http://tonto.eia.doe.gov/dnav/pet/hist/mcrexks2m.htm
U.S. Crude Oil Exports to Japan
http://tonto.eia.doe.gov/dnav/pet/hist/mcrexja2m.htm
U.S. Crude Oil Exports to China, Taiwan
http://tonto.eia.doe.gov/dnav/pet/hist/mcrextw2m.htm
Perhaps before the pipeline to Valdez was complete, or immediately thereafter?
Before the pipeline was built, I don't believe any crude oil left the North Slope by tanker in the short ice-free season. There isn't an export terminal on the Shallow North Shore.