The following map from Stratfor shows the major oil suppliers of the United States, from 1993 to 2015. At the beginning of the diagram Saudi Arabia is at the top, while at the end of it the Saudis have been replaced by the Canadians. Canada is by far the largest oil supplier of the United States. Saudi Arabia and Mexico are competing for the second place.
The United States banned oil exports in 1973, after the Arabs imposed an oil embargo against the United States, due to the US support to Israel during the Arab-Israeli war of 1973 (Israel VS Egypt+Syria). At the time the Israelis and the Iranians were very close allies. I mention that to explain why the Arabs of the Persian Gulf were very hostile towards Israel, even though at the time they hated the poor in oil Arabs of Egypt and Syria even more than the Israelis. See “The Intra-Arab War for Oil 1950-1970”. The Arabs also imposed an oil embargo on South Africa, which at the time was an ally of Israel and helped Israel during the war.
Now the United States are lifting the ban on oil exports, because its production has increased, but mainly because the European Union is putting pressure on US to do so, in order to have an alternative to the Russian oil and gas in case of a crisis with Russia. The American oil and gas will be expensive when compared to the Russian ones, but I guess during a crisis that would not really matter.
“Lifting Oil Ban Great for Renewable Energy”, 2015