The natural gas engine technology company, which keeps its books in U.S. dollars, said the loss amounted to 59 cents per share in its latest quarter compared with a loss of $13.2 million or 27 cents per share a year ago.
Revenue for the quarter slipped to $76.1 million from $81 million.
Shares in Westport fell nearly 15 per cent last month after it cut its expectations for revenue growth this year to about 30 per cent compared with earlier expectations for 50 per cent.
In its outlook, the company said it expected revenue between $340 and $350 million for 2012 down from earlier guidance for between $400 million and $425 million.
The company earned $264 million in revenue in 2011.
"The overall market for natural gas transportation is developing with more infrastructure in place by the end of this year and key product launches for the industry," Westport chief executive David Demers said in a statement.
"We may have changed our near-term and annual revenue expectations, however, recent announcements to bring a new Cummins Westport 6.7 litre engine to market, targeting school buses, and an innovative new engine with Tata, also prove the thesis that virtually all segments of the transportation market will see significant opportunity for natural gas this decade."
Westport develops engines that use fuels such as compressed natural gas, liquefied natural gas, hydrogen and renewable natural gas fuels such as landfill gas.
Shares in the company closed up 46 cents at $23.67 on the Toronto Stock Exchange on Thursday.