Shares in the Japanese automaker surged 8% on Thursday, the first day of gains since the scandal erupted last week. But even so they have lost nearly half their market value or about $3.7 billion on fears of hefty compensation costs and fines.

It has admitted to manipulating test data for four domestic mini-vehicle models, including two it produced for Nissan Motor and has said that more models may also be non-compliant with Japanese regulations.

It compiled data for fuel economy tests using U.S. standards, where higher-speed, highway driving is common, rather than Japanese standards, where more prevalent city driving commonly consumes more fuel.

Mitsubishi’s North American unit said in a statement that it had re-tested vehicles for the model years 2013 to 2017 and found that their fuel economy readings were accurate.

While North America is one of Mitsubishi’s smaller markets, accounting for roughly 13 percent of the automaker’s annual global sales, the potential for hefty fines and compensation if rules were broken is seen as much greater than in other countries.

In Japan, Mitsubishi (MMTOF) may have to reimburse customers for fuel costs and the government for “eco car” tax breaks.

It is also taking a large hit to sales, saying this week that its domestic orders have halved since the scandal broke. The automaker has halted sales of the four affected mini-vehicles.

Japan’s transport ministry said on Thursday it plans tests to measure the fuel economy of vehicles made by Mitsubishi next week and will announce results on the first four models in June.

It has also set up a task force to examine fuel economy data submitted by all automakers.