The Kingdom of Saudi Arabia is often cited as the world's largest oil producer. The country produces 13.24% of the oil consumed in the entire world daily. Saudi Arabia has the second-largest reserves of naturally occurring oil in the world after Venezuela. It is estimated that Saudi Arabia's oil resources amount to 260 billion barrels of oil.
However, if you take into account the production of biofuels and liquid fuel produced from natural gases as well as oil production, then the United States is the largest producer in the world. The U.S. has been at the forefront of extraction of natural shale gas, particularly at sites in North Dakota and Texas, and this has been instrumental in raising the country's national energy source production.
Oil is a precarious market, and there is always the possibility that another nation could overtake both Saudi Arabia and the U.S. as the largest international producer of oil. There is a quantity of untapped resources in Iraq, but discovery and refinement are currently being hindered because of terrorist activity and civil unrest. In addition, there are huge amounts of oil in African countries, such as Libya and Nigeria, which are also underdeveloped due to political upheaval and other problems.
There are also untapped resources in Northern Siberia, a Russian territory. Russia is currently the world's third largest producer of oil, and therefore it is entirely possible that the country could present a challenge in the future as a top oil producer.