Sales of vehicles able to drive themselves will account for about 9 percent of global auto sales in about two decades, according to a forecast published on Tuesday by auto industry consultant IHS Automotive.

The study focused on autonomous cars, which can drive with "no attention needed by the driver," IHS analyst Egil Juliussen said. Such cars are not currently available for sale, but IHS predicts they will be available around 2025.

IHS expects global sales of self-driving cars in 2025 to be 230,000 -- less than 1 percent of the 115 million cars expected to be sold that year.

But by 2035, sales of self-driving cars will reach 11.8 million, or 9 percent of the 129 million global auto sales expected that year, said Juliussen.

Most of these sales will be in well-established auto markets like the United States, Western Europe and Japan.

The pace of growth for self-driving cars will exceed that of electric cars, which have been hobbled by the high cost of batteries, Juliussen said.