More than 930,000 medium- and heavy-duty natural gas-powered trucks and buses are expected to be sold worldwide by 2019, according to a new report. Sales of natural-gas trucks are expected to grow at an annual rate of 14% though 2019, according to Pike Research. In Europe and North America, the high cost of diesel fuel and continued emissions restrictions are expected to boost sales of natural gas-fueled heavy-duty vehicles, the report said.