The U.S. shale oil revolution has increased production and helped keep oil prices from rising sharply, despite supply disruptions from other parts of the world.

But the North American shale success story isn’t good news for some African members of the Organization of Petroleum Exporting Countries (OPEC), especially Nigeria, Angola, and Algeria, and non-OPEC members such as Ghana and South Sudan.

The U.S., which a few years ago was the largest oil importer in the world, has drastically reduced its oil imports. The U.S. posted the biggest increase in oil production in the world and the largest in U.S. history in 2012 when production reached 8.9 million barrels (bbl.) per day, up 13.9% from 2011, according to the BP Statistical Review of World Energy.

U.S. output, adding to the world’s oil supply, has contributed to keeping oil prices from rising sharply in spite of supply disruptions from Nigeria, Iraq, Libya, South Sudan, and other key producers.

But Nigeria and Algeria, which produce light sweet crudes that are low in sulfur content and simple to refine, are already feeling the impact of the U.S. oil boom. They are the most impacted in terms of reduced oil exports to the U.S. and lower oil prices in the past year. These and other countries need high oil prices to support local spending.

U.S. imports from Nigeria were more than halved to 403,000 bbl. per day in March 2013, from 913,000 in March 2011, according to U.S. Energy Information Administration (EIA). Also, the EIA said exports from Angola to the U.S. from April 2011 to April 2012 dropped 38% to 4.8 millio bbl.

OPEC said in its annual report released in the first week of July 2013 that the price benchmark oil from some OPEC members fell in the past year because of the unexpected energy boom in the U.S., which is causing a revolution in global oil trade.

The average price of Algeria’s Saharan Blend on the spot market fell by 1.3% in 2012 to $111.49 a barrel, while Nigeria’s Bonny Light slipped 0.4% to average $113.66 a barrel, the report said.

“Shale oil has been identified as one of the most serious threats for African producers,” Nigeria’s Minister of Petroleum Resources Diezani Alison-Madueke said, adding that African producers could lose 25% of their oil revenue as they are edged out of the U.S. market.

Nigeria and Algeria are suffering the worst effects from the North American oil boom since they produce a grade similar to shale oil, she said, stressing that shale oil is a “grave concern.”

“We risk a situation where, in the first place, we lose our oil market in America. But beyond that we also risk a situation where America, having satisfied itself with what it has, will also want to find a market outside. And that market may be a market that Nigeria is selling to,” said Omar Farouk, general manager of media relations at the Nigerian National Petroleum Corp. (NNPC).

Commenting on U.S. shale oil on July 8, 2013 in Abuja, the Nigerian capital, Nigerian President Goodluck Jonathan said “Nigeria is known for oil. But today, many countries around the world have found oil. The recent discovery of shale oil and gas means that we can no longer depend solely on oil to drive the economy.”

During a five-day state visit to China at the beginning of July 2013, Jonathan met executives from Sinopec, which is China’s largest refiner, according to a statement from his office in Abuja. But it was not clear whether the president succeeded in getting China to increase its oil imports from Nigeria.

Nigeria and other African producers that produce light sweet crude may not have big market in Asia, because several Asian refiners process heavy crude produced by OPEC members in the Persian Gulf, said an oil expert in Lagos.

Angola, which produces around 1.72 million bbl. per day of oil, is already looking for new markets for oil, according to its Oil Minister Jose Maria Botelho de Vasconcelos. Rising hydrocarbons production in the U.S., Angola’s second main export market after China, also poses a threat to Angola, where the oil sector accounts for 45% of GDP, 75% of government revenue and more than 90% of total exports.

Algeria produced about 1.87 million bbl. per day of oil in 2012 and the vast majority of Algerian oil exports, roughly 85%, are sent to North America and Europe. The U.S. is the single largest destination; however, U.S. imports of Algerian crude have declined over the last five years.

The value of Algeria’s oil and gas exports fell by 9% in the first four months of 2013 compared to the same period in 2012 due to lower global crude oil prices, according to government figures published in a report by the country’s APS news agency.

Algeria’s Finance Minister Karim Djoudi said lower oil revenue, due to the U.S. shale oil revolution, could force the government to cut domestic spending and delay some projects if crude oil prices keep falling.

“Emerging markets like India and China have been growing, and they have absorbed a large part of Angolan exports,” said Botelho de Vasconcelos.

Rising U.S. oil production would have negative impacts on several African countries, especially if oil prices keep falling. These countries include Liberia, Uganda, and Kenya, which have discovered oil but have not started production. Oil investors in these countries may be discouraged. Exploration may slow down, pushing forward production time. Moreover, oil revenues expected by these countries may be lower than earlier expected, affecting their development programs.

Oil revenue earnings of OPEC and non-OPEC African oil producers and several other oil producers may be impacted further if China is successful in making the needed technological advances to tap its shale oil deposits, pumping more oil into the global market.

OPEC has promised to launch a study of the impact U.S. shale oil production is having on its members, OPEC’s Secretary General Abdalla Salem El-Badri said.

But ultimately it is up to OPEC members affected by shale oil output to seek out new markets on their own, El-Badri added.

The EIA has predicted the US will pump 11.1 MMb/d by 2020, surpassing Saudi Arabia, the world’s top oil exporter.