Venezuela is the worlds fourth largest oil exporter and fourth or fifth (depending on the time-frame) largest exporter to the U.S.
From the Wall Street Journal:
Venezuelan President Hugo Chávez's defeat in a referendum on changing the country's constitution will energize the nation's opposition, but the leader is likely to continue his quest to remain in power and turn the country into a bastion of what he calls 21st-century socialism.
Mr. Chávez's defeat in Sunday's vote shows a growing impatience among Venezuelans, including surprising numbers of Mr. Chávez's supporters, about his inability to substantially improve their lives, despite near-record-high oil prices and the fact that he has governed the country for nearly a decade. Mr. Chávez sought to amend the constitution of the world's ninth-largest oil producer to allow him to concentrate nearly all power, including scrapping limits on re-election.
Mr. Chávez's defeat will ripple across Latin America, hurting allies in countries like Bolivia and Ecuador and boosting moderates in Brazil and Chile. For the U.S. and Europe, a weaker Mr. Chávez is welcome news. The former military officer has been increasingly hostile to Western interests in the past few years, nationalizing key areas of the economy like the oil industry, telecommunications and utilities....MORE
Here's the EIA's Basic Petroleum stats page.