OPEC says that fossil fuels will remain the main energy source in the coming decades with coal's share growing and oil's falling.

In its annual World Oil Outlook, the Organization of the Petroleum Exporting Countries also projects that a barrel of benchmark crude will cost $155 by 2035, compared with under $100 now.

The report, published Thursday, says the use of fossil fuels as a percentage of world energy use will decrease only marginally from 87 percent now to 82 percent by 2035.

It says that by then, "coal use reaches similar levels as that of oil, with oil's share having fallen from 35 percent in 2010 to 27 percent by 2035."

The report notes there are more coal reserves — mostly in the U.S. — than oil and gas.