DETROIT — General Motors sold a record 9.92 million vehicles worldwide last year, a 2 percent increase from 2013 but below Volkswagen’s 10.1 million.

Volkswagen’s count included an unspecified number of larger heavy-duty trucks and commercial vehicles that GM did not include in its total.

Determining the global sales leader will have to wait until later this month when Toyota reports its tally. Last year, Toyota’s global sales were 10.32 million. Because the industry’s global sales rose about 4 percent last year, the chances are good that Toyota will repeat its world-leading performance from 2013.

Separately, John Murphy, Bank of America Merrill Lynch’s auto analyst, predicted that sales in the U.S. market will grow to an unprecedented 20 million new vehicles in 2018. If accurate, that would be a 21 percent increase from 2014’s total of 16.5 million. But they will drop sharply after that, based on a slide Murphy showed at the Automotive News World Congress.

Murphy’s outlook is considerably more bullish than other forecasts. He said it is based on what he sees will be a growing need for some buyers to replace aging vehicles. While U.S. new-vehicle sales have risen for five consecutive years, the average age of all cars and trucks on the road remains about 11 years.

Another factor that will contribute to industry growth for four more years is easy credit. Banks, finance companies and credit unions are approving loans for a growing percentage of car buyers with checkered credit histories.

While the federal government has requested documents from several lenders about their “subprime” lending practices, there is little evidence that the trend will stop.