From the EIA:

The amount of crude oil the United States imported from its top five foreign suppliers—Canada, Saudi Arabia, Mexico, Venezuela, and Nigeria—increased slightly during 2011, even though total U.S. crude oil imports fell to their lowest level in 12 years. As a result, the crude oil
from these five countries accounted for a bigger share of overall U.S. crude oil imports, nearly 69%, or just over 6.1 million barrels per day (bbl/d).

Canada, Saudi Arabia, Mexico, Venezuela, and Nigeria have consistently been America’s five largest crude oil suppliers, although their rankings varied from year to year. However, U.S. purchases of crude oil in 2011 increased from Canada and Saudi Arabia and declined from Mexico, Venezuela, and Nigeria, according to final trade data from EIA’s February 2012 Company Level Imports report.

Combined crude oil imports from the five countries increased by less than 1% during 2011 to 6.1 million bbl/d. At the same time, total U.S. imports fell about 3%, or 0.3 million bbl/d, to 8.9 million bbl/d. That marked the lowest annual level of crude oil imports for the United States since 1999.

The combination of lower total U.S. crude oil imports and higher crude oil shipments from the top five foreign suppliers boosted their market share to about 69% of all U.S. crude oil imports during 2011, compared to 66% in 2010.