Matt Krantz

USA TODAY

The Ebola outbreak in West Africa is disrupting some drilling plans for the USA's biggest oil company.

ExxonMobil CEO Rex Tillerson said at a press conference Thursday in Houston that the company is having second thoughts about plans to start offshore drilling in some areas in West Africa due to concerns.

USA TODAY was not present at the meeting, but company spokesman Patrick McGinn confirmed the comments first reported by Reuters in an e-mail to USA TODAY.

"Safety, health and logistical issues related to Ebola will delay the planned late 2014 start of ExxonMobil's first exploration well offshore Liberia," McGinn said.

The postponement will affect one well off the Liberian coast. Exxon's operations in Nigeria are not affected.

The company also said it is restricting non-essential travel by employees to the West African countries where the outbreak has struck. The hardest-hit countries are Liberia, Sierra Leone and Guinea, but the virus has also struck in Senegal and Nigeria.

Shares of Exxon closed up 44 cents, or 0.5%, at $93.30. Africa is home to 20% of Exxon's proven developed crude oil reserves and 3% of natural gas. Meanwhile, 20% of Exxon's proven undeveloped oil reserves are in Africa.

Few large U.S. companies have significant activity even in the sub-Saharan Africa region, of which only a portion is affected by the outbreak. Many of the companies that do business in the sub-Saharan Africa region are centered in South Africa, far from the region affected by the outbreak.

Seven companies have disclosed an undefined but notable presence in the sub-Saharan region, says S&P Capital IQ. They are Accenture (ACN), American International Group (AIG), Chevron (CVX), Cisco Systems (CSCO), Citigroup (C), Morgan Stanley (MS) and Starwood Hotels (HOT).

Their exact exposure to Ebola-affected countries is not clear:

• Accenture, a global consulting firm, lists South Africa as one of its priority emerging markets. Accenture's revenue from emerging-markets nations, which include Asia as well as Africa, accounted for 40% of revenue in fiscal 2013.

• American International Group, an insurer, lists Johannesburg Insurance Holdings as a significant unit. Last year, AIG's emerging-markets business wrote $6.8 billion in property casualty policies, accounting for 20% of the total.

• Chevron, the energy company, competes with Exxon in Africa. The company in 2013 reported net production of 431 oil-equivalent barrels a day in Africa, which was 17% of its total.

• Cisco Systems the networking company also maintains a presence in South Africa. Revenue from Cisco's African business is consolidated with its emerging markets, including Asia. Total emerging markets revenue in the year ended July 26 was 26% of total revenue.

• Citigroup, the global financial firm, has been aggressive in the emerging world. Revenue from emerging markets, which includes Africa, accounted for 41% of Citi's revenue in 2013. And trouble in emerging nations has caused the company to relocate staff before, the company says in its annual regulatory filing.

• Morgan Stanley, the global investment bank, operates a unit out of South Africa. Revenue from the region isn't nearly as significant to Morgan Stanley as it is to Citi. Revenue from Africa, combined with Europe and the Middle East was $4.5 billion in 2013, or 14% of total revenue.

• Starwood Hotels operates and franchises hotels all over the world, including 85 in Africa and the Middle East. Those properties account for 7% of the company's 1,175 worldwide properties at the end of last fiscal year.

Starwood's stock was among the hardest hit travel stocks Wednesday as investors reacted to the confirmation of an Ebola-infected patient in the U.S. Shares closed down 81 cents, or 1.0%, to $79.39 Thursday. That's after falling 3.6% on Wednesday.