In the previous week ending Oct. 19, WTI and Brent lost 3.7 percent and 1.2 percent, respectively, and WTI and Brent settled at 69.12 U.S. dollars and 79.78 dollars per barrel, respectively, at the end of the week.
On Monday, U.S. oil prices inched up 0.07 percent despite vow of Saudi Arabia to enhance oil production. WTI grew 0.05 U.S. dollar to settle at 69.17 dollars a barrel, and Brent edged up 0.05 dollars to 79.83 dollars per barrel.
There has been concern that in the context of the U.S. sanctions against Iran, which are now set to take effect on Nov. 4, Saudi Arabia could cut crude supply in retaliation for potential sanctions against it over the disappearance of Saudi journalist Jamal Khashoggi.
Analysts fear Saudi retaliation would cause supply shock, sending oil prices up. But on Monday, trying to dismiss such concerns, Saudi Arabia's Energy Minister Khalid Al-Falih said that "there is no intention" for such action, and that Saudi Arabia would play a "constructive and responsible role" in world energy markets.
Saudi Arabia would also raise its daily crude oil output to 11 million barrels from 10.7 million barrels and the country has a capacity to generate 12 million barrels of crude oil each day, according to Al-Falih.
On Tuesday, U.S. oil prices further dived 4.22 percent as Saudi Arabia vowed to enhance oil production and U.S. stock markets sank on disappointing earnings reports. WTI lost 2.93 U.S. dollars to settle at 66.43 dollars a barrel, and Brent sank 3.39 dollars to 76.44 dollars per barrel.
The U.S. stock market lost over 2 percent in the early session resulting from warning of higher production costs by heavy equipment maker Caterpillar Inc. and disappointing operating results of industrial conglomerate 3M Corporate in the third quarter.
Moreover, Saudi Arabia's Energy Minister Khalid al-Falih said on Tuesday that the Organization of the Petroleum Exporting Countries (OPEC) and its partners are in "produce as much as you can" mode.
On Wednesday, U.S. oil prices rebounded 0.59 percent on fall of gasoline and diesel stockpiles in the previous week in the United States. WTI gained 0.39 U.S. dollar to settle at 66.82 dollars a barrel, while Brent further decreased 0.27 dollar to 76.17 dollars per barrel.
U.S. commercial crude oil stockpiles in the week ending Oct. 19 rose 6.3 million barrels week on week while total petroleum inventories dropped as much as 8 million barrels, according to data issued by the U.S. Energy Information Administration (EIA) on Wednesday.
Meanwhile, gasoline and distillate fuel inventories fell 4.8 million barrels and 2.3 million barrels, respectively, which bolstered oil prices.
In terms of future oil prices, EIA's latest October Short-Term Energy Outlook (STEO) forecast that Brent crude oil spot prices, which averaged 70 dollars per barrel in September, are expected to average 81 dollars per barrel in the fourth quarter of 2018 and will fall to an average of 75 dollars per barrel in 2019.
EIA also forecast WTI prices to increase at a slightly slower rate, leading to a widening of the Brent-WTI spread to 9 dollars per barrel in October. But the spread would narrow to 4 dollars per barrel by December 2019.
What's more, EIA said the higher crude oil prices at the end of 2018 and in 2019 will likely support increased global crude oil production. EIA forecast that U.S. crude oil production to increase by 1 million barrels per day in 2019. EIA also forecast that total global liquid fuels inventories to decrease by 200,000 barrels per day in 2018, followed by an increase of 280,000 barrels per day in 2019.
However, the effects of the U.S. withdrawal from the Joint Comprehensive Plan of Action (JCPOA) in May, the resumption of Iran sanctions and the potential response from other countries pose significant uncertainty to the forecast.
On Thursday, oil prices rose as investors were encouraged by a strong rebound in the U.S. stock markets. WTI increased 0.51 dollar to settle at 67.33 dollars a barrel, while Brent added 0.72 dollar to 76.89 dollars a barrel.
U.S. stocks suffered big losses Wednesday, with the Dow Jones Industrial Average sinking over 600 points, which raised concerns that a possible slowdown in global economic growth could reduce oil demand.
However, U.S. equities rebounded strongly on Thursday, with the Nasdaq Composite Index jumping about 3 percent in late trading, soothing anxious investors to some extent.
On Friday, crude oil futures prices of the United States gained 0.39 percent on concerns over less supply from Iran. WTI picked up 0.26 dollar to settle at 67.59 dollars a barrel. Meanwhile, Brent further increased 0.74 dollars to 77.63 U.S. dollars per barrel.
U.S. sanctions on Iranian crude oil exports would take effect on Nov. 4, prompting more countries to cut imports from Iran. Still, U.S. crude oil futures prices lost 2.2 percent for the week, marking the third straight weekly loss.
The United States has 875 operating oil drilling rigs in this week, adding two more from the previous week, according to data issued by oil service company Baker Hughes on Friday.
There are also signs of a slowdown in global trade, with container and bulk freight rates dropping after rising for most of 2018, according to reports.
In the coming weeks, traders keep a close eye on U.S. sanctions on Iranian crude exports. Concerns about the gap in crude oil supply caused by U.S. sanctions on Iran have fueled spike of crude oil prices in the past few months.
Because of the concerns about possible shortage of supply due to U.S. sanctions on Iran, the oil market is also beginning to be worried about possible oversupply and inventories that are rising in many other parts of the world.
Meanwhile, the market will focus on the news of any meeting between officials from China and the United States aiming at seeking solution to the ongoing trade tensions.